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Data Communications Reference
Electronic User’s Manual
Registered Company
Winona, Minnesota USA
Watlow Controls
1241 Bundy Blvd., P.O. Box 5580, Winona, Minnesota USA 55987-5580, Phone: (507) 454-5300, Fax: (507) 452-4507
WTCDCE_A.pdf Made in the U.S.A.
June 1998 $15.00
Safety Information
We use note, caution and warning symbols throughout this book to draw your attention to important operational and safety information.
A “ NOTE” marks a short message to alert you to an important detail.
A “ CAUTION” safety alert appears with information that is important for protecting your equipment and performance. Be especially careful to read and follow all cautions that apply to your application.
A “ WARNING” safety alert appears with information that is important for protecting you, others and equipment from damage. Pay very close attention to all warnings that apply to your application.
The safety alert symbol, , (an exclamation point in a triangle) precedes a general CAUTION or
WARNING statement.
The electrical hazard symbol, , (a lightning bolt in a triangle) precedes an electric shock hazard
CAUTION or WARNING safety statement.
Technical Assistance
If you encounter a problem with your Watlow controller, review all of your configuration information to verify that your selections are consistent with your application: inputs; outputs; alarms; limits; etc. If the problem persists after checking the above, you can get technical assistance from your local Watlow representative, or by dialing (507) 454-5300, ext. 1111. An applications engineer will discuss your application with you.
Please have the following information available when calling:
• Complete model number (from the label on the side of the controller)
• All configuration information,
User Profile Record, Custom Main Page Record and Operations Page Parameter Record
• User’s Manual
• Diagnostic Menu readings (if applicable)
About Watlow Controls
Watlow Controls is a division of Watlow Electric
Mfg. Co., St. Louis, Missouri, a manufacturer of industrial electric heating products since 1922.
Watlow begins with a full set of specifications and completes an industrial product that is manufactured in-house, in the U.S.A. Watlow products include electric heaters, sensors, controllers and switching devices. The Winona operation has been designing solid-state electronic control devices since
1962, and has earned the reputation as an excellent supplier to original equipment manufacturers.
These OEMs and end users depend upon Watlow
Controls to provide compatibly engineered controls that they can incorporate into their products with confidence. Watlow Controls resides in a 100,000square-foot marketing, engineering and manufacturing facility in Winona, Minnesota.
Your Feedback
Your comments or suggestions on this manual are welcome. Please send them to the Technical
Literature Team, Watlow Controls, 1241 Bundy
Blvd., P.O. Box 5580, Winona, Minnesota, 55987-
5580; phone: (507) 454-5300; fax: (507) 452-4507.
The Watlow Controls Data Communications Guide is copyrighted by Watlow Winona, Inc., © June 1998, with all rights reserved. (1454)
T
Table of Contents
Chapter 1
Audience . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
Media . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4
Purpose . . . . . . . . . . . . . . . . . . . . . . . . . . . .4
Getting Started . . . . . . . . . . . . . . . . . . . . . . .4
Convention . . . . . . . . . . . . . . . . . . . . . . . . . .4
Chapter 2
Elements of Machine to Machine Comm. . . .5
Character Format . . . . . . . . . . . . . . . . . . . . .5
Bits and Bytes . . . . . . . . . . . . . . . . . . . . . . .5
ASCII . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5
ASCII Chart . . . . . . . . . . . . . . . . . . . . . . . . .6
Serial Communication . . . . . . . . . . . . . . . . . .7
Parity Bits . . . . . . . . . . . . . . . . . . . . . . . . . . .7
Start and Stop Bits . . . . . . . . . . . . . . . . . . . .8
Baud Rate . . . . . . . . . . . . . . . . . . . . . . . . . .8
Computer Languages . . . . . . . . . . . . . . . . . .8
Syntax . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8
Chapter 3
Interface Standards . . . . . . . . . . . . . . . . . . .9
Wiring . . . . . . . . . . . . . . . . . . . . . . . . . . . . .9
Biasing of Buses . . . . . . . . . . . . . . . . . . . . . .9
Interface Converters . . . . . . . . . . . . . . . . . .10
Protocols . . . . . . . . . . . . . . . . . . . . . . . . . .10
Chapter 4
Write Your Own (HMI) . . . . . . . . . . . . . . . . .12
Purchase an HMI package . . . . . . . . . . . . .18
Chapter 5
Interface Adapters . . . . . . . . . . . . . . . . . . .20
Watlow Software Tools . . . . . . . . . . . . . . . .20
922 Comm Diagnostic . . . . . . . . . . . . . . . .21
Comm4 Diagnostic Software . . . . . . . . . . . .21
Comm5vb Diagnostic Software . . . . . . . . . .21
CRC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .21
Interface Comparison . . . . . . . . . . . . . . . . .22
Controller Comparison Summery . . . . . . . .22
Appendix
Glossary . . . . . . . . . . . . . . . . . . . . . . . . . . .23
Disclaimer of Warranty . . . . . . . . . . . . . . . .28
A downloadable electronic copy of this user manual is available free of charge through Watlow's web site: http://www.watlow.com/prodtechinfo
Wa t l o w C o n t r o l s C o m m u n i c a t i o n G u i d e 3
Chapter One -
Introduction
Audience
The document is targeted towards new users interested in using data communications with Watlow controllers.
Media
This document is available in electronic format only. It is viewable using Adobe
Acrobat Reader available free from the
Adobe site www.adobe.com
on the
World Wide Web.
Purpose
The purpose of this document is to enable users to:
1. Understand the basics of serial data communications via standard definitions, interfaces and protocols.
2. Set up and use a simple network of one
Watlow controller.
3. Set up and use a network of two or more Watlow controllers with HMI
(human-machine interface) software or an operator interface panel.
Getting Started
Your task is to get one or more controllers to talk to a PC or PLC. How do you make this happen? The purpose of this document is to assist you in that task by providing information about communications. The task of getting a PC or PLC communicating with controllers is a five step process:
1. Determine a strategy for communications.
2. Purchase a controller with a communication interface and protocol that supports your strategy.
3. Wire controllers for power, control and communication.
4. Configure the controllers to do what you want them to do.
5. Configure the PC or PLC software and hardware to do what you want them to do.
The first step is the most difficult since decisions need to be made before anything is purchased. It really involves three basic items:
1. Determine how many controllers you will communicate with.
2. Pick a protocol and interface that supports the information exchange.
3. Purchase hardware and software to make this happen.
This document will only deal with the task of communication. Refer to the user’s manuals for each product for information about wiring and configuring the controllers and software.
Convention
In this document, numbers in the format
0x00 represent values in hexadecimal.
Numbers in the format 0 represent values in decimal and finally, numbers in the format 00000000 represent values in binary unless stated otherwise.
Watlow Controls Communications Guide 4
Chapter 2 -
Definition of Terms
Elements of Machine-to-
Machine Communication
In human communication there are basic words and sentences used to get a message across. Likewise, with computers and controllers. They need a code called a character format or character set. They need rules called protocol to govern their conversation and prevent confusion and errors. Computers need a connecting interface over which to communicate.
They may use one pair of wires to send information in one direction and another pair to send in the opposite direction (full duplex). Or they may use one pair to send in both directions (half duplex).
Character Format
The code or character formats for Watlow data communication is shared by virtually everyone in the electronics business everywhere. This code defines a computer stream of 1’s and 0’s, that are created by varying a voltage signal in a regular manner. The code is the American
Standard Code for Information
Interchange, called ASCII (asky).
Bits and Bytes
The word bit is simply the contraction of the words binary digit . A bit is the basic unit in ASCII. It is either a “1” or a “0”.
A byte is a string of seven or eight bits that a computer treats as a single character. ASCII requires seven bits to represent each letter of the alphabet, each digit and each punctuation mark we use.
ASCII
The ASCII code defines 128 separate seven- or eight-bit characters (see chart below), one for each letter, digit and punctuation mark. ASCII also includes control characters similar to those we find on computer keys, such as backspace, shift and return. It also has nine communications control characters for identification, enquiry (inquiry), start of text, end of text, end of transmission, acknowledge, negative acknowledge and escape.
The ASCII code is sometimes written in a base-16 number system that is called hexadecimal or “hex” for short. The numbers 0 through 9 represents the first ten digits of this system, and the letters A through F represents the final six digits.
The 128 ASCII character code with the decimal and hexadecimal equivalents is listed below.
Watlow Controls Communications Guide 5
Dec Hex
3C
3D
3E
3F
38
39
3A
3B
34
35
36
37
30
31
32
33
2C
2D
2E
2F
28
29
2A
2B
24
25
26
27
20
21
22
23
1C
1D
1E
1F
18
19
1A
1B
14
15
16
17
10
11
12
13
0C
0D
0E
0F
08
09
0A
0B
04
05
06
07
00
01
02
03
ASCII
Char
>
?
<
=
;
:
8
9
6
7
4
5
2
3
0
1
/
.
-
,
*
+
)
(
$
%
‘
&
“
#
!
SP
FS
GS
RS
US
CAN
EM
SUB
ESC
DLE
DC1
DC2
DC3
DC4
NAK
SYN
ETB
FF
CR
SO
SI
BS
HT
LF
VT
NUL
SOH
STX
ETX
EOT
ENQ
ACK
BEL
60
61
62
63
56
57
58
59
52
53
54
55
48
49
50
51
44
45
46
47
40
41
42
43
36
37
38
39
32
33
34
35
28
29
30
31
24
25
26
27
20
21
22
23
16
17
18
19
12
13
14
15
08
09
10
11
04
05
06
07
00
01
02
03
The first digit in bold is the parity bit when enabled.
7 bit w/ Even
Parity
00000000
10000001
10000010
00000011
10000100
00000101
00000110
10000111
10001000
00001001
00001010
10001011
10011100
00011101
00011110
10011111
10100000
00100001
00100010
10100011
00100100
10100101
10100110
00100111
00101000
10101001
10101010
00101011
00001100
10001101
10001110
00001111
10010000
00010001
00010010
10010011
00010100
10010101
10010110
00010111
00011000
10011001
10011010
00011011
10101100
00101101
00101110
10101111
00110000
10110001
10110010
00110011
10110100
00110101
00110110
10110111
10111000
00111001
00111010
10111011
00111100
10111101
10111110
00111111
No Parity
7 or 8 bit
00110000
00110001
00110010
00110011
00110100
00110101
00110110
00110111
00111000
00111001
00111010
00111011
00111100
00111101
00111110
00111111
00100000
00100001
00100010
00100011
00100100
00100101
00100110
00100111
00101000
00101001
00101010
00101011
00101100
00101101
00101110
00101111
00010000
00010001
00010010
00010011
00010100
00010101
00010110
00010111
00011000
00011001
00011010
00011011
00011100
00011101
00011110
00011111
00000000
00000001
00000010
00000011
00000100
00000101
00000110
00000111
00001000
00001001
00001010
00001011
00001100
00001101
00001110
00001111
ASCII Chart
7 bit w/ Odd
Parity
ASCII
Char
Dec
10000000
00000001
00000010
10000011
00000100
10000101
10000110
00000111
00001000
10001001
10001010
10011011
00011100
10011101
10011110
00011111
00100000
10100001
10100010
00100011
10100100
00100101
00100110
10100111
10101000
00101001
00101010
00001011
10001100
00001101
00001110
10001111
00010000
10010001
10010010
00010011
10010100
00010101
00010110
10010111
10011000
00011001
00011010
10101011
00101100
10101101
10101110
00101111
10110000
00110001
00110010
10110011
00110100
10110101
10110110
00110111
00111000
10111001
10111010
00111011
10111100
00111101
00111110
10111111
{ z x y
}
|
~
DEL t u v w r s p q n o l m j k i h f g d e b c
` a
^
_
]
\
[
Z
X
Y
T
U
V
W
R
S
P
Q
N
O
L
M
J
K
I
H
F
G
D
E
B
C
@
A
120
121
122
123
124
125
126
127
112
113
114
115
116
117
118
119
104
105
106
107
108
109
110
111
96
97
98
99
100
101
102
103
92
93
94
95
88
89
90
91
84
85
86
87
80
81
82
83
76
77
78
79
72
73
74
75
68
69
70
71
64
65
66
67
7C
7D
7E
7F
78
79
7A
7B
74
75
76
77
70
71
72
73
6C
6D
6E
6F
68
69
6A
6B
64
65
66
67
60
61
62
63
5C
5D
5E
5F
58
59
5A
5B
54
55
56
57
50
51
52
53
4C
4D
4E
4F
48
49
4A
4B
44
45
46
47
40
41
42
43
Hex No Parity
7 or 8 bit
01110000
01110001
01110010
01110011
01110100
01110101
01110110
01110111
01111000
01111001
01111010
01111011
01111100
01111101
01111110
01111111
01100000
01100001
01100010
01100011
01100100
01100101
01100110
01100111
01101000
01101001
01101010
01101011
01101100
01101101
01101110
01101111
01010000
01010001
01010010
01010011
01010100
01010101
01010110
01010111
01011000
01011001
01011010
01011011
01011100
01011101
01011110
01011111
01000000
01000001
01000010
01000011
01000100
01000101
01000110
01000111
01001000
01001001
01001010
01001011
01001100
01001101
01001110
01001111
7 bit w/ Odd
Parity
01110000
11110001
11110010
01110011
11110100
01110101
01110110
11110111
11111000
01111001
01111010
11111011
01111100
11111101
11111110
01111111
11100000
01100001
01100010
11100011
01100100
11100101
11100110
01100111
01101000
11101001
11101010
01101011
11101100
01101101
01101110
11101111
11010000
01010001
01010010
11010011
01010100
11010101
11010110
01010111
01011000
11011001
11011010
01011011
01011100
01011101
01011110
11011111
01000000
11000001
11000010
01000011
11000100
01000101
01000110
11000111
11001000
01001001
01001010
11001011
01001100
11001101
11001110
01001111
7 bit w / Even
Parity
11110000
01110001
01110010
11110011
01110100
11110101
11110110
01110111
01111000
11111001
11111010
01111011
11111100
01111101
01111110
11111111
01100000
11100001
11100010
01100011
11100100
01100101
01100110
11100111
11101000
01101001
01101010
11101011
01101100
11101101
11101110
01101111
01010000
11010001
11010010
01010011
11010100
01010101
01010110
11010111
11011000
01011001
01011010
11011011
01011100
11011101
11011110
01011111
11000000
01000001
01000010
11000011
01000100
11000101
11000110
01000111
01001000
11001001
11001010
01001011
11001100
01001101
01001110
11001111
Watlow Controls Communications Guide 6
Serial Communication
The interfaces we’ve chosen employ serial communication, which is the exchange of data in a one-bit-at-a-time, sequential manner on a single data line or channel.
Serial contrasts with parallel communication, which sends several bits of information simultaneously over multiple lines or channels. Not only is serial data communication simpler than parallel, it is also less costly
ASCII Control Codes
ASCII Control Codes are used to give instructions to the remote device and result in specific actions, such as a line feed instruction on a printer.
ASCII Control Codes, the first 33
ASCII characters (non printable), are important for the operation of communicating equipment. They give instruction to remote devices that result in specific actions such as a line feed on a printer Holding down the keyboard control key while pressing the appropriate keyboard key will send these values.
ASCII
Char
Dec Hex Ctrl Key
Equiv.
NUL 00 00 Crtl @
SOH 01 01 Crtl A
STX 02 02 Crtl B
ETX 03 03 Crtl C
EOT 04 04 Crtl D
ENQ 05 05 Crtl E
ACK 06 06 Crtl F
BEL 07 07 Crtl G
BS
HT
LF
VT
08 08 Crtl H
09 09 Crtl I
10 0A Crtl J
11 0B Crtl K
FF 12 0C Crtl L
CR 13 0D Crtl M
SO 14 0E Crtl N
SI 15 0F Crtl O
DLE 16 10 Crtl P
Definition ASCII
Char
Dec Hex Ctrl Key
Equiv.
Null Character
Start of Header
Start of Text
End of Text
DC1 17 11 Crtl Q
DC2 18 12 Crtl R
DC3 19 13 Crtl S
DC4 20 14 Crtl T
End of Transmission NAK 21 15 Crtl U
Enquiry SYN 22 16 Crtl V
Acknowledge
Bell
ETB
CAN
23
24
17
18
Crtl W
Crtl X
Back Space EM 25 19 Crtl Y
Horizontal Tabulation SUB 26 1A Crtl Z
Line Feed
Vertical Tabulation
ESC
FS
27
28
1B
1C
Crtl [
Crtl \
Form Feed
Carriage Return
Shift Out
Shift In
Data Link Escape
GS
RS
US
SP
29
30
31
32
1D
1E
1F
20
Crtl ]
Crtl |
Crtl _
Parity Bit
Remember that ASCII is a seven- or eightbit code. What about that eighth bit? It’s called the parity bit. A parity bit is added to the ASCII character to verify the accuracy of the first seven bits. We are declaring that the number of 1s in the 8bit character frame will be either always odd or always even.
This way we can detect a single error in the seven-bit group. Take a look at the representation of the transmitted upper case “W.” In this case we have selected
“odd” parity. The number of 1s in the first seven bits, plus the parity bit, must always total an odd number. The total number of 1s in the binary character
1010111 (W) is 5, already an odd number.
Thus our parity bit will be a 0.
Definition
Data Control 1 - XON
Data Control 2
Data Control 3 - XOFF
Data Control 4
Negative Acknowledge
Synchronous Idle
End of Trans Block
Cancel
End of Medium
Substitute
Escape
File Separator
Group Separator
Record Separator
Unit Separator
Space
If we were transmitting the lower case “w”
(binary 1110111), the parity bit would be a 1 because the total number of 1’s in the character frame is 6, an even number.
Adding the parity bit makes it odd, and consistent with the odd parity rule.
If a noise spike came onto the data line and changed the signal voltage level enough to reverse a 1 to a 0 in the character frame, the receiver would detect that error. The total number of 1s would be even and a violation of the odd-parity rule.
At Watlow, we use odd, even and no parity.
Odd parity sets the parity bit to 0 if there are an odd number of 1s in the first seven bitsEven parity sets the parity bit to 0 if there are an even number of 1s in the first seven bits.
No parity ignores the parity bit.
Watlow Controls Communications Guide 7
Start and Stop Bits
A start bit informs the receiving device that a character is coming, and a stop bit tells it that a character is complete. The start bit is always a 0. The stop bit is always a 1.
The human speech equivalent of these bits could be a clearing of the throat to get someone’s attention (start bit); and a pause at the end of a phrase (stop bit).
Both help the listener understand the message.
Baud Rate
The baud rate refers to the data transmission. When a change in signal represents one data bit, baud rate is equal to bits per second (bps). Standard baud rates for computers are 300, 600, 1200,
2400, 4800, 9600 and 19200 baud.
Computer Languages
Computer languages are simply sets of symbols and rules for their use. There are many computer languages and a wide variety of applications for them.
Programmers use languages to enable computers to do real work.
Syntax
Syntax for a natural language dictates how we put words together to make phrases and sentences. In data communications, syntax also dictates how we order the parts of a message.
Watlow Controls Communications Guide 8
Chapter Three -
Watlow Controls
Approach to Data
Communications
Interface Standards
An interface is a means for electronic systems to interact. It’s a specific kind of electrical wiring configuration. Four interfaces are commonly used:
EIA-232 (Full Duplex)
An EIA-232 (formerly RS-232) interface uses three wires: a single transmit wire; a single receive wire; and a common line.
Only two devices can use an EIA-232 interface. A -3 to -24 volt signal indicates a 1 and a +3 to +24 volt signal indicates a
0. The EIA-232 signal is referenced to the common line rather than to a separate wire, as in EIA-485 and EIA-422. An
EIA-232 cable is limited to 50 feet, due to noise susceptibility.
EIA-422 (Full Duplex)
The EIA-422 interface uses five wires: a
“talk” pair; a “listen” pair; and a common line. It can handle one master and up to ten remote devices in a multidrop (more than one controller shares the same wires) network up to 4,000 feet long. EIA-422 uses the difference in voltage between the two wires to indicate a 1 or a 0 bit. A 1 is a difference of -5 volts, while a 0 is a difference of +5 volts.
EIA-423 (Full Duplex)
An EIA-423 interface is compatible with
EIA-232. It is a newer standard designed for more speed and distance. It uses three wires: a single transmit wire; a single receive wire; and a common line. Only two devices can use an EIA-423 interface.
A -3 to -6 volt signal indicates a 1 and a
+3 to +6 volt signal indicates a 0. The
EIA-423 signal is referenced to the
Watlow Controls Communications Guide 9 common line rather than to a separate wire, as in EIA-485 and EIA-422. An
EIA-423 cable is limited up to 4,000 feet, due to noise susceptibility.
EIA-485 (Half Duplex)
An EIA-485 interface uses three wires: a
T+/R+, a T-/R- and a common line. A -5volt signal is interpreted as a 1, a +5-volt signal as a 0. As many as 32 remote devices can be connected to a master on a multi-drop network up to 4,000 feet long.
Wiring
Most PCs and some PLCs have a standard
EIA-232 port (usually referred to as RS-
232). In these instances, you must use an interface converter to connect to EIA-
422 or EIA-485. These interface standards are required to have a multi-drop system
(more than one controller on the bus). See the list below for some vendors who sell these converters.
Should your PC or PLC have the appropriate interface, just connect using the wiring diagram supplied with your controller.
For EIA-422, the T+ connects to the R+, sometimes labeled “B” while the Tconnects to the R- , sometimes labeled
“A”. For EIA-485, the terminal marked
“A” usually connects to the T-/R- while the “B” terminal connects to the T+/R+ of the controller.
The standards do not specify the wire size and type. Use of AWG 24 twisted pair provides excellent results. If shielded cable is used, terminate the shield at one end only.
Always follow the manufacturer’s instructions supplied with the interface converter. See Biasing of Buses next.
Biasing of Buses
The EIA-485 standard requires the bus to be biased for reliable communication. This means to provide termination resistors
across the T+/R+ and T-/R- wires. One resistor is placed at the PC or PLC where it connects to the EIA-485 bus. The second resistor is placed at the last controller on the network. Do not place resistors at each controller. The impedance of the wires used for the bus determines the resistor value. For twisted pair, the value is typically 120 ohms. In addition, it may be necessary to have a pull-up and pull-down resistor between the power supply and ground of the interface adapter. Check the documentation that came with your interface adapter.
Biasing the bus reduces reflection of signals sent down the bus. These reflections are sometimes referred to as a standing wave.
This condition is most notable when communicating at high baud rates.
Interface Converters
The purpose of an interface converter is to allow two different buses to be connected. Interface converters are required when connecting an EIA-232 port to an EIA-422 or EIA-485 bus.
The EIA-422 bus is a full duplex bus. This means that it can send and receive data at the same time. The EIA-485 bus is a half duplex bus. This means that it can only send or receive data at any given time.
Some interface converters on the market have provided the ability to have full duplex with the EIA-485 bus. This is accomplished by using two receivers and transmitters tied in tandem. This type of converter will not work with the Watlow controllers. Be sure that the model you purchase is designed for half duplex.
Another consideration when using interface converters is how the converter handles switching between transmit and receive. When connecting between an
EIA-232 and an EIA-485, the converter must convert two items. First it must convert the voltage level. Second it must convert from half duplex to full duplex.
This is not an easy task. Typically it is accomplished via a handshake line from
Watlow Controls Communications Guide 10 the PC or PLC. When data flows into the converter from the PC, a handshake line is placed high. When data flows out of the converter to the PC, the handshake line is placed low. In this way, the handshake line controls the direction of information.
Another method of achieving this is to use a built-in timer. The converter switches to transmit when a character is sent to it from the PC. After a period of time when the PC has not transmitted, the converter switches to a receive mode.
It is important that you understand how your converter accomplishes this task.
You are required to wire this feature or make settings on the converter to enable this function. The PC will not talk to the controllers correctly with out properly setting this.
Your converter may also require settings through dip switches, to set up communications parameters like baud rate, data bits, start bits, stop bits and handshaking. See the documentation that comes with your converter for more detail.
The converter may require a separate power supply. Some converters get their power from the handshake lines of the PC.
If you rely on this method, you will need to wire these additional lines. In addition, your software must set these lines high. A more reliable method is to use the external power supply. This is especially necessary when using a laptop computer.
Protocols
Protocol describes how to initiate an exchange. It also prevents two machines from attempting to send data at the same time. There are a number of different data communications protocols, just as there are different human cultural protocols that vary according to the situation.
The protocol part of Watlow communications is very important, because it gives us a quality of communication that others often don’t have. Protocol-driven communications
are more accurate, because they are less prone to both operator and noise errors.
Protocol maintains system integrity by requiring a response to each message. It’s like registered mail — you know that your letter has been received because the post office sends you a signed receipt.
In Watlow data communications, a dialog will continue successfully as long as the messages are in the correct form and responses are returned to the protocol leader. If the operator enters an incorrect message, or interference comes on to the data line, there will be no response. In that case the master must retransmit the message or go to a recovery procedure. If an operator continues to enter an incorrect message or interference continues on the data line, the system will halt until the problem is resolved.
Watlow provides you with three protocol choices: XON/XOFF, ANSI x3.28, Modbus
RTU
XON/XOFF
The first protocol is conventional
XON/XOFF protocol. It works very well for systems that do not require a message response and for those with only two devices (one PC and one controller).
Sending of the "XON" (0x11) and "XOFF"
(0x13) controls information. This is the simplest protocol offered by Watlow
Controls.
ANSI x3.28
The second, called “Full Protocol,” is based on the American National Standard
Institute’s standard ANSI X3.28-1976,
Subcategory 2.2. The Full Protocol is required for systems that need a response to every message, and for any “multidrop” network, which has more than two communication devices. Addressing a certain controller on the bus, then enclosing all messages with a <STX> start of text (0x02) and <ETX> end of text
(0x03) controls information exchange.
The characters <ENQ>, <EOT>, <DLE> are used to determine who has control of the bus. Lastly, all messages are <ACK>
Watlow Controls Communications Guide 11 acknowledged (0x06) or <NAK> negative acknowledged (0x15) to ensure messages where received correctly.
Modbus Remote Terminal Unit
(RTU)
Gould Modicon, now called AEG
Schneider, created the third protocol for process control systems called "Modbus".
This protocol is the most complex of the three. It has the advantage of being extremely reliable in exchanging information, a highly desirable feature for industrial data communications. This protocol works on the principle of packet exchanges. The packet contains the address of the controller to receive the information, a command field that says what is to be done with the information and several fields of data. Reading from these registers retrieves all information in the controller. These registers are listed in your user’s manual. You will need this list to determine where the data is located.
The last item sent in the packet is a field to ensure the data is received intact. This is called a cyclic redundancy check-sum.
All information exchanged is in hex numbers. Watlow only supports the binary version of Modbus, referenced as RTU.
The ASCII version is less efficient and is not supported.
Chapter Four -
Human Machine
Interfaces (HMI)
HMI stands for Human-Machine-
Interface, and is sometimes referred to as
Man-Machine-Interface (MMI). This is an operator interface that allows you to monitor and control your process. Many software packages were written to allow a
PC to perform this function. Use care in selecting software packages. Some will run only under a specific disk operating system such as Windows NT from Microsoft. The serial interface and protocol must match between the PC or PLC and the controller.
Many companies provide free working demonstration copies. Obtain a demonstration copy so you can see if the program meets your needs.
Listed below are a few of the many software packages that claim to support the Modbus protocol. Watlow does not recommend any one software package nor supports the implementation of any software package not sold by Watlow.
Contact the software manufacturer for more information in applying their software.
Write your own HMI
Writing an XON/XOFF
Application
The great thing about XON/XOFF protocol is the simplicity of communications. The basic structure is to send information to the controller as needed until you receive an XOFF (0x13).
You must wait until you receive an XON
(0x11) before continuing. The controller follows this same scheme. There are no confirmations of commands sent. This protocol is highly efficient in that few characters are sent to handle the flow of information. This protocol is sometimes referred to as “flow control”.
The disadvantage of this protocol is lower reliability in ensuring that both parties receive the proper information. In addition, only two devices can be on a bus because no means is provided to address any controller.
Handling Error Codes (ER2)
All communications' related error codes are ER2 error codes, which means that they're not considered cause for a shutdown of the unit itself. With
XON/XOFF flow control, error codes may be generated, but there will be no standard indication of this fact. Therefore, you may want to query the status of ER2 after each command sent to see if it was successful.
User Responsibility
Users must refrain from altering prompts that do not appear on the controller’s front panel or are not included on the specific model. For example, do not send an A2LO command to a unit not equipped with an alarm for output 2.
Most Watlow controllers contain a register to disable saving of the current set point to EEPROM. When using your PC or PLC to control the set point in the
Watlow controller, the EEPROM may be prematurely damaged. There is a limit to the number of times you can store information in the EPPROM. PCs can quickly reach this limit if the set point is continually changed, as in a ramping controller. Disabling this feature will prevent this damage.
Care must also be taken that the process can not cause damage to property or injury to personnel if the wrong commands are sent due to operator error or equipment malfunction. Be sure to use limit devices on the equipment to prevent system runaway.
Writing an ANSI x3.28 Application
Handling Error Codes (ER2)
All communications' related error codes are ER2 error codes, which means that
Watlow Controls Communications Guide 12
they're not considered cause for a shutdown of the unit itself. There is always a communications error code generated when the <NAK> character
(0x15) is sent under the ANSI x3.28
protocol
User Responsibility
Users must refrain from altering prompts that do not appear on the controller’s front panel or are not included on the specific model. For example, do not send an A2LO command to a unit not equipped with an alarm for output 2.
Most of Watlow controllers contain a register to disable saving of the current set point to EEPROM. When using your PC or PLC to control the set point in the
Watlow controller, the EEPROM may be prematurely damaged. There is a limit to the number of times you can store information in the EPPROM. PCs can quickly reach this limit if the set point is continually changed, as in a ramping controller. Disabling this feature will prevent this damage.
Care must also be taken that the process can not cause damage to property or injury to personnel if the wrong commands are sent due to operator error or equipment malfunction. Be sure to use limit devices on the equipment to prevent system runaway.
Because of the wide array of choices available for setting up a Watlow controller, only a subset of the prompts contains parameters in a given situation.
The user's manual explains the interrelations between prompts.
Writing a Modbus Application
Modbus RTU enables a computer or PLC to read and write directly to registers containing the controller’s parameters.
With it you could read all 141 of the controller’s parameters with five read commands.
Because of the wide array of choices available for setting up a controller
Watlow Controls Communications Guide 13 utilizing Modbus, only a subset of the prompts contain parameters in a given situation. This document explains the interrelations between prompts.
If you already have a software application that uses Modbus, you can simply skip to the Temperature/process Controller
Prompt Table or the Modbus RTU Address
Table in the user’s manual for the address information your program will need. The rest of this section on the Modbus provides information for writing a software application that uses Modbus.
1. You need to code messages in eight-bit bytes, with no parity bit, one stop bit
(8, n, 1).
2. Negative parameter values must be written in twos' complement format.
Parameters are stored in two-byte registers accessed with read and write commands to a relative address.
3. Messages are sent in packets that are delimited by a pause at least as long as the time it takes to send 30 bits. To determine this time in seconds, divide
30 by your baud rate.
4. Because changing some parameters automatically changes or defaults other parameters, use the Complete
Parameter Download Sequence table listed in the user's manual to order write commands.
Using a controller address of 0x00 for a write command, will send that command to all the controllers in the network. This is a powerful feature if all the controllers on a network use all or most of the same parameters.
Packet Syntax
Each message packet begins with a one-byte controller address, from 0x01 to 0xF7.
The second byte in the message packet identifies the message command: read
(0x03 or 0x04); write (0x06 or 0x10); or loop back (0x08).
The next n bytes of the message packet contain register addresses and/or data.
The last two bytes in the message packet contain a two-byte Cyclical Redundancy
Checksum (CRC) for error detection.
Packet format: nn | nn | nnnn… | nn nn address command registers and/or data
CRC
Read Multiple Registers Command (0x03 or 0x04)
This command returns from 1 to 32 registers.
Packet sent to controller:| nn | 03 | nn nn | 00 nn | nn nn | controller address (one byte) read command (0x03 or 0x04) starting register high byte starting register low byte number of registers high byte (0x00) number of registers low byte
CRC low byte
CRC high byte
Packet returned by controller: | nn | 03 | nn | nn nn … nn nn | nn nn | controller address (one byte) read command (0x03 or 0x04) number of bytes (one byte) first register data low byte first register data high byte
…
… register n data high byte register n data low byte
CRC low byte
CRC high byte
Watlow Controls Communications Guide 14
Example (988 only): Read register 0 (model number) of the controller at address 1.
Sent: 01 03 00 00 00 01 84 0A
Received: 01 03 02 03 DC B9 2D
Message: 988 (0x03DC).
Example (988 only): Read register 1 and 2 (Process 1 and 2 values) of controller at address 5.
Sent: 05 03 00 01 00 02 94 4F
Received: 05 03 04 00 64 00 C8 FF BA
Message: 100 (0x0064) and 200 (0x00C8).
Write to a Single Register Command (0x06)
This command writes a parameter to a single register. The controller will echo back the command. An attempt to write to a read-only parameter returns an illegal data address error (0x02). (See “Exception Responses,” pg. 4.9.)
Packet sent to controller:| nn | 06 | nn nn | nn nn | nn nn | controller address (one byte) write to a register command (0x06) register high byte register low byte data high byte data low byte
CRC low byte
CRC high byte
Example (988 only): Set register 7 (SPI) to 200 (0x00C8) on controller at address 9.
Sent: 09 06 00 07 00 C8 38 D5
Received: 09 06 00 07 00 C8 38 D5
Write to Multiple Registers Command (0x10)
This command actually writes a parameter to only a single register. An attempt to write to a read-only parameter returns an illegal data address error (0x02). (See
“Exception Responses,” pg. 4.9.)
Packet sent to controller:| nn | 10 | nn nn | 00 01 | 02 | nn nn | nn nn | controller address (one byte) write to multiple registers command (0x10) starting register high byte starting register low byte number of registers to write high byte (0x00) number of registers to write low byte (must be 0x01) number of data bytes (must be 0x02) data high byte data low byte
CRC low byte
CRC high byte
Watlow Controls Communications Guide 15
Packet returned by controller: | nn | 10 | nn nn | 00 01 | nn nn | controller address (one byte) write to multiple registers command (0x10) starting register high byte starting register low byte number of registers to write high byte (0x00) number of registers to write low byte (must be 0x01)
CRC low byte
CRC high byte
Loop Back Command (0x08)
This command simply echoes the message. This serves as a quick way to check your wiring.
Packet sent to controller:| nn | 08 | nn nn | nn nn | controller address (one byte) loop back command (0x08) data high byte data low byte
CRC low byte
CRC high byte
Example: Run loop back test on controller at address 40 (0x28).
Sent: 28 08 55 66 77 88 31 B7
Received: 28 08 55 66 77 88 31 B7
Exception Responses
When a controller cannot process a command it returns an exception response and sets the high bit (0x80) of the command.
0x01 illegal command
0x02 illegal data address
0x03 illegal data value
Packet returned by controller: | nn | nn | nn | nn nn | controller address (one byte) command + 0x80 exception code (0x01 or 0x02 or 0x03)
CRC low byte
CRC high byte
Watlow Controls Communications Guide 16
Messages with the wrong format, timing or CRC are ignored. A read command sent to an inactive parameter returns 0x0000.
Example: Exception 01 - Command 02 is not supported.
Sent: 01 02 00 01 00 02 A8 0B
Received: 01 82 01 81 60
Example: Exception 02 - The parameter at register 45 (0x002D) is inactive.
Sent: 01 06 00 2D 00 01 D8 C3
Received: 01 86 02 C3 A1
Example: Exception 03 - Cannot write 12,000 (0x2EE0) to register 7, out of range, illegal data value.
Sent: 01 06 00 07 2E E0 24 23
Received: 01 86 03 02 61
Special Modbus Functions
The following are Modbus registers with special functions: 24, Disable Non-volatile (system)
Memory; 106, Alarm Status Output 2; 110, Alarm
Status Output 3; 114, Alarm Status Output 4; 200,
Auto-Manual Operation Mode; 311, Clear Input
Errors; 331, Clear Alarms; 332, Silence Alarms.
A "0" indicates an inactive state. Send "1" to the register to activate the function. It will automatically reset to "0" when the function is complete. See your
User’s Manual for detail on your specific model.
Watlow Controls Communications Guide 17
Handling Error Codes
Error codes are divided into two types.
Read error codes and write error codes are called exception codes. Reading from a register that does not exist or is currently disabled will typically respond with a large out of range value such as -32000, -32001, or -32002. The Series 988 returns a value of zero.
Writing to a register that is not supported, is inactive or out of range will return a packet with 0x80 added to the command sent. The byte following this will contain the value 0x01 for illegal command, 0x02 for illegal address, or 0x03 for illegal data value. Writing to a read only register will return an exception code 0x02.
See your user's manual for exact values and definitions.
User Responsibility
Users must refrain from altering prompts that do not appear on the controller’s front panel or are not included on the specific model. For example, do not send an A2LO command to a unit not equipped with an alarm for output 2.
Most of Watlow controllers contain a register to disable saving of the current set point to EEPROM. When using your PC or PLC to control the set point in the
Watlow controller, the EEPROM may be prematurely damaged. There is a limit to the number of times you can store information in the EPPROM. PCs can quickly reach this limit if the set point is continually changed, as in a ramping controller. Disabling this feature will prevent this damage.
Care must also be taken that the process can not cause damage to property or injury to personnel if the wrong commands are sent due to operator error or equipment malfunction. Be sure to use limit devices on the equipment to prevent system runaway.
Purchase an HMI package
Not all HMIs are equal in performance. Set up and operation / function of each
Watlow Controls Communications Guide 18 manufacturer’s HMI package is unique.
Industrial controllers operate in a harsh, electrically noisy environment. This can cause less robust HMIs to work intermittently or not at all. In addition, the platform (PC or PLC) which runs the
HMI is subject to failures causing unpredictable operation of your process.
Watlow has not tested the HMIs listed with the exception of ANAWIN and
WATLINK. This list is provided as informational only. Watlow makes no claims as to the performance or compatibility with any HMI software package.
Anawin by Watlow Anafaze
334 Westridge Drive
Watsonville, CA 95076
Phone 408-724-3800 http://www.watlow.com
WATLINK by Watlow Controls
1241 Bundy Blvd
Winona, MN 55987
Phone 507-454-5300 http://www.watlow.com
CONTROLWARE by Controlware
245 Northland Blvd
Cincinnati, OH 45246-3603
Phone 800-776-9704 http://www.controlware.com
Cimplicity by GE Fanuc
Phone 1-800-648-2001 http://www.gefanuc.com
Genesis by Iconics
100 Foxborough Blvd
Foxborough, MA 02035
Phone 800-946-9679 http://www.iconics.com
Interact by CTC
50 W. TechneCenter Drive
Milford, OH 45150
Phone 513-831-2340 http://www.ctcusa.com
KEPware MMI by KEPware, Inc.
81 Bridge Street
Yarmouth, ME 04096
Phone 207-846-5881
http://www.kepware.com
LabView by National Instruments
6504 Bridge Point Parkway
Austin, TX 78730-5039
Phone 512-794-0100 http://www.natinst.com
Lookout by National Instruments
6504 Bridge Point Parkway
Austin, TX 78730-5039
Phone 512-794-0100 http://www.natinst.com
Modbus for Windows by Calta
Computer Systems Ltd.
230, 550-71 Ave. SE
Calgary, Alberta Canada T2H 0S6
Phone 403-252-5094 http://www.calta.com
OI-2000 by Software Horizons, Inc.
10 Tower Office Park
Suite 200
Woburn, MA 01801-2120
Phone 617-933-3747 http://www.shorizons.com
SpecView by SpecView, LLC
41 Canyon Green Court
San Ramon, CA 94583
Phone 510-275-0600 http://www.specview.com
Watlow Controls Communications Guide 19
Visual Logic Controller by Steeplechase
Software, Inc.
1330 Eisenhower Place
Ann Arbor, MI 48108
Phone 313-975-8100 http://www.steeplechase.com
Wonderware 2000 by Wonderware
Corp.
100 Technology Drive
Irvine, CA 92718
Phone 714-727-3200 http://www.wonderware.com
Chapter Five -
Operator Interface
Panels
Not all Operator Interface Panels are equal in performance. Programming of each manufacturer’s panel is unique. Industrial controllers operate in a harsh, electrically noisy environment. This can cause less robust panels to work intermittently or not at all. Watlow has not tested the panels listed and this list is provided as informational only. Watlow makes no claims as to the performance or compatibility with any Operator Interface
Panel.
EXOR
4740T Interstate Drive
Cincinnati, OH 45246
Phone 513-874-4665 http://www.exor-rd.com
CTC
50 W. TechneCenter Drive
Milford, OH 45150
Phone 513-831-2340 http://www.ctcusa.com
Maple Systems
1930 220
th
Street SE
Suite 101
Bothell, WA 98021
Phone 425-486-4477 http://www.maple-systems.com
Advantech
Phone 1-800-800-6889 http://www.advantech-usa.com
Interface Adapters
Not all converters are equal in performance. Industrial controllers
Watlow Controls Communications Guide 20 operate in a harsh, electrically noisy environment. This can cause less robust converters to work intermittently or not at all. Watlow has not tested the converters listed and this list is provided as informational only. Watlow makes no claims as to the performance or compatibility with any converter .
B&B Electronics
707 Dayton Road
PO Box 1040
Ottawa, IL 61350
Phone 815-433-5100 http://www.bb-elec.com
Part # 485OIC for EIA-232 to EIA-422 or EIA-485
Dataforth Corporation (formerly supplied by Burr-Brown)
3331 E. Hemisphere Loop
Tucson, AZ 85706
Phone 800-444-7644
Part # LDM422 for EIA-232 to EIA-422
Part # LDM485 for EIA-232 to EIA-485
CMC – Connecticut Microcomputer
Corporation
Watlow Software Tools
920Comm Diagnostic
Software
Watlow has a program available free of charge called “920COMM.EXE” that is used with the Series 920 Controller. This can be downloaded from our BBS at 507-
452-3958. This is a terminal program that handles the protocol for you. The program can be used to determine if your cables are properly connected and that the controller is working. This program supports the ANSI x3.28 and XON/XOFF protocols.
922Comm Diagnostic
Software
Another program available free of charge is called “922COMM.EXE" which is used with the Series 922 Controller. This can be downloaded from our BBS at 507-452-
3958. This is a terminal program that handles the protocol for you. The program can be used to determine if your cables are properly connected and that the controller is working. This program supports the ANSI x3.28 and XON/XOFF protocols.
Comm4 Diagnostic Software
The “COMM4.EXE” program can be downloaded free of charge from our BBS at
507-452-3958. This is a terminal program which handles the protocol for you. The program can be used to determine if your cables are properly connected and that the controller is working. This program supports the ANSI x3.28 and XON/XOFF protocols.
Comm5vb Diagnostic
Software
The “COMM5VB.EXE” program can be downloaded free of charge from our BBS at
507-452-3958. This is a terminal program that handles the protocol for you. The program can be used to determine if your cables are properly connected and that the controller is working. This program supports the Modbus, ANSI x3.28 and
XON/XOFF protocols.
CRC
Cyclical Redundancy Checksum (CRC)
Algorithm
This C routine, calc_crc(), calculates the cyclical redundancy checksum, CRC, for a string of characters. The CRC is the result of dividing the string by 0xA001. Modbus applications calculate the packet’s CRC then append it to the packet.
#define POLYNOMIAL 0xA001; unsigned int calc_crc(unsigned char
*start_of_packet, unsigned char
*end_of_packet)
{ unsigned int crc; unsigned char bit_count; unsigned char *char_ptr;
/* Start at the beginning of the packet */ char_ptr = start_of_packet;
/* Initialize CRC */ crc = 0xffff;
/* Loop through the entire packet */ do{
/* Exclusive-OR the byte with the CRC */ crc ^= (unsigned int)*char_ptr;
/* Loop through all 8 data bits */ bit_count = 0; do{
/* If the LSB is 1, shift the CRC and XOR the polynomial mask with the CRC */ if(crc & 0x0001){ crc >>= 1; crc ^= POLYNOMIAL;
}
/* If the LSB is 0, shift the CRC only */ else{ crc >>= 1;
}
} while(bit_count++ < 7);
} while(char_ptr++ < end_of_packet); return(crc);
}
Watlow Controls Communications Guide 21
Interface Comparison
Interface Maximum Max #
EIA-423 4,000 feet 1
EIA-422 4,000 feet 10
EIA-485 4,000 feet 32
Cable Voltage
Standard Bus Length Controllers Type Level
EIA-232 50 feet 1 3-wire 3 – 24 v
Balanced/ Duplex
Unbalanced
Unbalanced Full
3-wire 3 – 12 v Unbalanced Full
5-wire 2.0 – 6 v Balanced Full
3-wire 1.6 – 6 v Balanced Hal
Summary
As first stated in this article, the steps involved to communicate are:
1. Determine how many controllers you will communicate with
2. Pick a protocol and interface that supports the information exchange
3. Purchase hardware and software to make this happen.
The number of controlled zones will determine the number of controllers connected to the PC or
PLC. Pick a protocol that will support this number. Consider speed and reliability of communications when picking the protocol. Ask yourself, how will the devices understand each other? Pick an interface that will support the number of devices connected, transmit over the desired distance and is industrially hardened
(will communicate in electrically noisy environments). Lastly, purchase an interface, controllers, PC or PLC and software that will work together. Software may be written to accomplish the task if you have the skills and resources to do so.
Watlow Controls Communications Guide 22
Appendix
Glossary
Address
A unique designator for a location of data or a controller that allows each location or controller on a single communications bus to respond to its own message. Similar to your own residence address.
ANSI
ANSI x3.28
The American National Standards Institute developed this communication standard protocol. This method uses a unique address for each device. Only the master can initiate a communications session by sending an address and then the <ENQ> character. All other messages must start with a start of text <STX> and end with an end of text <ETX> character. The bus is released to the other device by sending
<EOT> character. Messages are <ACK> acknowledged or <NAK> negative acknowledged.
ASCII (pronounced AS-KEY)
American Standard Code for Information
Interchange. A universal standard for encoding alphanumeric characters into 7 or 8 binary bits.
Asynchronous
Communications where characters can be transmitted at an unsynchronized point in time. In other words, it can start and stop anytime. The time between transmitted characters may be of varying lengths.
Communication is controlled by “start” and “stop” bits at the beginning and end of each character.
Baud
Unit of signaling speed derived from the number of events per second (normally bits per second).
Baud rate
The rate of information transfer in serial communications, measured in bits per second.
Watlow Controls Communications Guide 23
Binary
Number based system where only two characters exist, 0 and 1. Counting is 0, 1, 10, 11...
Bit condition in the binary system.
Byte
A term referring to eight associated bits of information, sometimes called a “character”.
CAN Bus
The communications protocol that includes software and hardware. CAN was originally developed by the German company Robert Bosch for use in the auto industry to provide a cost-effective communications bus for in-car electronics.
Character
Letter, numeral, punctuation, control figure or any other symbol contained in a message.
Typically this is encoded in one byte.
Communications
The use of digital computer messages to link components. (See serial communications and baud rate)
Converter
This device will convert from one hardware interface to another such as from EIA-232 to EIA-
485. The converter may be transparent to the software, which means you do not have to give any special considerations to software programming.
CRC
When data is corrupted during transmission, a method is used to return the data to its correct value. This can be accomplished through several methods: parity, checksum and CRC (cyclic mechanism using a polynomial algorithm based on the content of a message frame at the transmitter and included in a field appended to the frame. At the receiver, it is then compared with the results of the calculation that is performed by the receiver.
Data
The information that is transferred across the communications bus. This may be a setpoint, setup parameter, or any character. This information is transferred to an address or register.
DB-9
A standardized connector shaped like the letter “D” when viewed on edge. This connector has 9 contacts. It is utilized on most IBM AT compatible PCs as the serial port.
DB-15
A standardized connector shaped like the letter “D” when viewed on edge. This connector has 15 contacts. It is utilized on most IBM AT compatible PCs as the game/midi port.
DB-25
A standardized connector shaped like the letter “D” when viewed on edge. This connector has 25 contacts. It is utilized on most IBM AT compatible PC’s as the parallel port when the PC end contains socket contacts. Can also be the serial port when the PC end contains pin contact.
Decode
This is the reverse of encode. When a piece of data has information embedded in it, decode is to extract that information.
Ex. To extract an “A” from 01000001.
DeviceNet
A software protocol / hardware interface based on CAN. A low cost communication link that connects industrial devices over a network. Uses twisted pair wires for the power and bus. Nodes can be removed or inserted on the bus without powering down the network.
Double Word
Equivalent to two words or four bytes.
This equals 32 bits.
Duplex
The ability to send and receive data at the same time. “To listen and talk at the same time.”
EIA
See Electronic Industries Association
EIA-232
Electronic Industries Association developed this standard hardware interface to allow one device to talk to another device in full duplex mode. This method uses a differential voltage between one wire and ground. Also called an unbalanced system since the ground wire carries the sum of current of all lines. First standard to gain wide acceptance by manufacturers.
Transmission is limited to about 50 feet.
EIA-422
Electronic Industries Association developed this standard hardware interface to allow up to 10 devices to be on a bus at one time. This method uses a differential voltage between two wires. Also called a balanced system since each wire carries the same current values. This has the advantage of being immune to outside electrical disturbances.
EIA-423
Electronic Industries Association developed this standard hardware interface to allow one device to talk to another device in full duplex mode. This method uses a differential voltage between one wire and ground. Also called an unbalanced system since the ground wire carries the sum of current of all lines. This standard is compatible with EIA-232. The outputs were beefed up to allow transmission up to
4000 ft.
EIA-485
Electronic Industries Association developed this standard hardware interface to allow up to 32 devices to be on a bus at one time. This method uses a differential voltage between two wires. Also called a balanced system since each wire carries the same current value. This has the advantage of being immune to outside electrical disturbances.
EIA/TIA -232, -422, -423 and -485
Data communications standards set by the
Electronic Industries Association and
Telecommunications Industry Association.
Watlow Controls Communications Guide 24
Formerly referred to as RS-
(Recommended Standard). (See EIA-232,
EIA-422, EIA-423 and EIA-485)
Electronic Industries Association
(EIA)
An association in the US that establishes standards for electronics and data communications
Encode
To embed information into a piece of data. This is the reverse of decode. Ex.
Let’s let 01000001 stand for an “A”.
Error Correction
When an inconsistency is in the data, a method is used to detect and/or return the data to its correct value. This can be done through several methods, parity, checksum and CRC (cyclic redundancy checksum) are a three of these.
Ethernet
A local area network developed by Xerox in the early 70’s and standardized by
Xerox, Digital Equipment and Intel in
1978. This is a serial communications method which all devices share the lines.
An address is sent in a packet to talk to a device on the line. This protocol supports peer-to-peer communications.
Even
This term is used with parity. See parity.
Fieldbus
The term fieldbus is a general definition for an industrial network media that resides at the machine level and below in a total network system. The primary purpose of this network is to interconnect the machine level and sublevel control functions and services in a distributive topology. It is not a particular protocol or physical connection system. Included in this generalization definition are standard protocols of Profibus, Modbus, DeviceNet,
SDS, WorldPIP, and P-Net.
Firmware
Instruction or data stored in an IC
(integrated circuit) or on a read only disk.
This data is programmed once and cannot easily be changed as software can.
Full
See Full Duplex.
Full Duplex
Full is used to mean the duplex’s full capability. The ability to send and receive data at the same time. The same as duplex.
GPIB
See IEEE488
Half Duplex
The ability to send or receive data, but not at the same time. “To listen or talk, but not both at the same time.”
Handshake (Handshaking)
Exchange of predetermined signals between two devices establishing a connection. Using extra wires or software signals to coordinate communications, signals can be sent to tell the transmitter the current status of the other device receiver. Ex. Are you busy or are you ready?
Hex or Hexadecimal
Number based system where sixteen characters exist, 0 to 9, A to F. Counting is 0..9,A,B,C..
HMI
Human to Machine Interface typically performed in software on a personal computer. Also called MMI.
IEEE488
Bus developed by Hewlett-Packard in 1965 as HP-IB. Also referred to as GPIB
(General Purpose Interface Bus). Consist of 8 data lines and 8 control lines. Bus length limited to 20.0 meters. Supports 15 devices on the bus at one time.
Logic Level
A voltage measurement system where only two stable voltage values exist. Ex. 0v and
5V, or -3v and +3v.
Watlow Controls Communications Guide 25
Mark
Represents the transmission of data bit logic 1 (see logic level). Usually this is the most negative voltage value in serial communications.
Master
The device on the bus that controls all communications. Only the master can initiate conversation.
Modbus
A software protocol developed by Gould
Modicon (now AEG) for process control systems. No hardware interface is defined.
Modbus is accessed on the master/slave principle, the protocol providing for one master and up to 247 slaves. Only the master can initiate a transaction. This is a half duplex protocol.
MMI
Man to Machine Interface typically performed in software on a personal computer. Also called HMI.
Network
When two or more devices share communications lines, the devices are
“networked”.
Node
A point of interconnection to a network.
Noise Immunity
The ability of communications lines to ignore electrical noise generated in the communications lines by nearby magnetic and electrostatic fields.
Odd
This term is used with parity. See parity.
OSI
Open Systems Interconnection are those which conform to specifications and guidelines that are open to all. This allows equipment from any manufacturer, which claims to comply with the standard, to be used interchangeably on the standard network.
Parallel
Communication using this method, transfers eight bits or one byte at a time over eight data wires and one ground wire.
This method is eight times faster than using serial but utilizes more hardware.
Parity
A bit is assigned at the beginning of a byte to stand for parity. When the ‘1’ bits are counted, the number will be even or odd.
A parity bit is used to ensure that the answer is always even if even parity or odd if odd parity. If the receiving end counts the ‘1’ bits and the sum is not the same odd or even, an error is generated. Ex.
00010000 has an odd number of 1s. In even parity, we would set the parity to 1 so we have an even number of bits. In odd parity, we would set the parity bit to 0 so we have an odd number of ‘1’ bits. Parity is used to detect errors caused by noise in data transmission.
PC
Personal Computer, coined by IBM when it introduced its first IBM PC Jr., which later became PC, XT, AT, 286, 386, 486,
Pentium, Pro, MMX Pentium, and latest
Pentium II.
Peer to Peer
Two devices that can talk to each other.
Both devices can initiate communications.
This may also be called Master-to-Master communications.
Profibus
Profibus is actually three buses. Profibus
FMS (Field Message Specification),
Profibus PA (Process Automation), and
Profibus DP (Process Periphery). FMS is a higher level bus intended to operate with
PLCs, Pcs and higher level nodes. Profibus
DP supports three masters. The masters then operate with field nodes as master-toslaves. Profibus PA is an intrinsically safe bus. The protocol is essentially the same as DP but the electrical / physical specifications are modified to satisfy low voltage and current requirements.
Watlow Controls Communications Guide 26
Protocol
A set of rules for communication. This will specify what method to transfer information, packet size, information headers and who should talk when. It is used to coordinate communication activity.
Receive
To accept data sent from another device.
The device that receives the data is the receiver.
Register
An area of memory that provides temporary storage of digital data.
RJ11
A connector used on most telephones that has four terminals.
SDS
Smart Distributed System is a CAN based device-level control network that can be scan or event driven, configured as masterslave or peer-to-peer, and can support devices of varying complexity. . Uses twisted pair wires for the power and bus.
Slave
A device that only responds to commands.
This device never starts communication on it’s own. Only the Master can do this.
(See Master)
SCADA
Supervisory Control and Data Acquisition
Serial
To process something in order. First item, second item, etc.
Serial Communications
A method of transmitting information between devices by sending all bits serially
(see serial) over a single communication channel.
EIA/TIA-232
(Formerly RS-232) -
An Electronic Industries Association
(EIA)/Telecommunication Industry
Association (TIA) standard for interface
Watlow Controls Communications Guide 27 between data terminal equipment and data communications equipment for serial binary data interchange. This is usually for communications over a short distance (50 feet or less) and to a single device.
EIA/TIA-485 (Formerly RS-485) –
An Electronic Industries Association
(EIA)/Telecommunication Industry
Association (TIA) standard for electrical characteristics of generators and receivers for use in balanced digital multi-point systems. This is usually used to communicate with multiple devices over a common cable or where distances over 50 feet are required.
Software
Information of data or program stored in an easily changeable format. (RAM,
Floppy Disk, Hard Disk)
Space
Represents the transmission of a data bit logic 0 (see logic level). Usually this is the most positive voltage value in serial communications.
Start Bit
A binary bit or logic level that represents when the serial data information is about to start (at the beginning of a character or byte). This voltage level is positive.
Stop Bit
A binary bit or logic level that represents when the serial data information is complete (at the end of a character or byte). This voltage level is negative.
Synchronous
When data is transmitted on a data line and a clock signal is used on another line to determine when to check the data line for a logic level. This clock is said to
“synchronize” the data.
TCP/IP
Transmission Control Protocol/Internet
Protocol is a software protocol used to send and receive data between different computer systems. Standard protocol used on the Internet.
Transmit
To send data from one device to another.
The device that sends the data is the transmitter.
Word
Two bytes make a word. This contains 16 bits.
XON/XOFF
A software protocol that controls the flow of serial information. Sending an XON tells the transmitter to start sending information. An XOFF tells the transmitter to stop sending until the receiver has processed the current information. XOFF = DC3 = Control S = hex 11, XON = DC1 = Control Q = hex
13.
Disclaimer of Warranty
This is a general overview and statement of the safety-related need for and methods of applying "data comunications for temperature processes." Because of the diversity of conditions and hazards under which control products may be applied, and because of the differences in components and methods of their installation, no representation or warranty of any kind, express or implied, is hereby made, that the data comunications discussed and presented herein will be effective in any particular application or set of circumstances, or that additional or different precautions will not be reasonably necessary for a particular application. We will be pleased to consult with you regarding a specific application upon request.
Trademark Information
Watlow®, Gordon®, Anafaze®,
ANASOFT®, ANAWIN®, MICRODIN are trademarks of Watlow Electric
Manufacturing Company.
Modbus™ is a trademark of AEG
Schneider Automation.
Windows® and Microsoft® are trademarks of the Microsoft Corporation.
Watlow Controls Communications Guide 28
Index
A
B
C
Comm5vb Diagnostic Software 21
Controller Comparison Summery 22
D
E
Elements of Machine to Machine
G
I
M
P
S
W
Wa t l o w C o n t r o l s C o m m u n i c a t i o n s G u i d e 2 9
How to Reach Us
Contact
Your Authorized Watlow Distributor:
Quality and
Mission
Statement:
Watlow Controls will be the world’s best supplier of industrial temperature control products, services and systems by exceeding our customers’, employees’ and shareholders’ expectations.
• Phone: (507) 454-5300.
• Fax: (507) 452-4507.
• For technical support, ask for an Applications Engineer.
• To place an order, ask for Customer Service.
• To discuss a custom option, ask for a Product Manager.
Warranty
Most Watlow Controls are warranted to be free of defects in material and workmanship for 36 months after delivery to the first purchaser for use, providing that the units have not been misapplied. Since Watlow has no control over their use, and sometimes misuse, we cannot guarantee against failure. Watlow's obligations hereunder, at Watlow's option, are limited to replacement, repair or refund of purchase price, and parts which upon examination prove to be defective within the warranty period specified. This warranty does not apply to damage resulting from transportation, alteration, misuse or abuse.
Returns
• Call or fax Customer Service for a Return Material Authorization (RMA) number before returning a controller.
• Put the RMA number on the shipping label, and also on a written description of the problem.
• A restocking charge of 20% of the net price is charged for all standard units returned to stock.
Watlow Controls Communications Guide
Watlow Controls, 1241 Bundy Blvd., P.O. Box 5580, Winona, Minnesota USA 55987-5580,
Phone: (507) 454-5300, Fax: (507) 452-4507
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Table of contents
- 1 Data Communications Guide
- 2 Safety Information
- 2 Technical Assistance
- 2 About Watlow Controls
- 2 Your Feedback
- 3 Table of Contents
- 4 Chapter One
- 4 Audience
- 4 Media
- 4 Purpose
- 4 Getting Started
- 4 Convention
- 5 Chapter 2
- 5 Elements of Machine-to-Machine Communication
- 5 Character Format
- 5 Bits and Bytes
- 5 ASCII
- 6 ASCII Chart
- 7 Serial Communication
- 7 Parity Bit
- 8 Start and Stop Bits
- 8 Baud Rate
- 8 Computer Languages
- 8 Syntax
- 9 Chapter Three
- 9 Interface Standards
- 9 Wiring
- 9 Biasing of Buses
- 10 Interface Converters
- 10 Protocols
- 12 Chapter Four
- 12 Write your own HMI
- 20 Chapter Five
- 20 Interface Adapters
- 20 Watlow Software Tools
- 20 920Comm Diagnostic Software
- 21 922Comm Diagnostic Software
- 21 Comm4 Diagnostic Software
- 21 Comm5vb Diagnostic Software
- 21 CRC
- 22 Interface Comparison
- 22 Controller Comparison Summary
- 23 Appendix
- 29 Index
- 30 How to Reach Us
- 30 Warranty
- 30 Returns