9 Building the Communication Cable Building the Cable

9 Building the Communication Cable Building the Cable
99
Building the Cable
Building the Communication Cable
There are several considerations that help determine the type of cable needed for
your D2–DCM application.
1. Will the D2–DCM be physically connected in a point-to-point configuration
or multi-drop configuration?
2. What electrical specification is best for your application? RS232C or
RS422?
3. What is the cable schematic?
4. What are the relevant cable specifications?
5. What installation guidelines are necessary?
The next few pages discuss these considerations in detail.
Tip: If you need a quick test cable you may want to try our FA–CABKIT which allows
you to quickly build several different types of cables. (See page 15 for more
information). If you’re fairly comfortable with network or communications cabling
requirements, see Appendix A for detailed diagrams.
Data Communications Module, 2nd Edition, 2/03
10
Building the Cable
Consideration 1:
Physical
Configuration
The D2–DCM can be used in either a point-to-point or multi-drop configuration. A
point-to-point connection only has two stations, a master and a slave. Use the
point-to-point configuration to connect a personal computer, an operator interface,
or an intelligent device to a single D2–DCM. You must also use this configuration
when you want to connect a DirectNET master station to a single DirectNET slave
station.
Use the multi-drop configuration to connect one master to two or more slaves (90
slave maximum).
Point to Point
or
DCM
D2–DCM
DL205 Master
DirectNET PLC Slave
Multi-drop
DirectNET
Masters
DirectNET Slaves
or
D2–DCM
Data Communications Module, 2nd Edition, 2/03
11
11
Building the Cable
Consideration 2:
Electrical
Specification
RS232C or RS422
The D2–DCM can support RS232C or RS422 communication. Your application and
configuration choice will help determine which electrical specification is best for you. If
you are using multi-drop, you must use RS422. If you are using point-to-point, you may
have a choice between RS232C and RS422.
You can use RS232C if the cable length is less than 50 feet and if the cable will not be
subjected to induced electrical noise that is commonly found near welders, large motors,
or other devices that create large magnetic fields.
You must use RS422 for all other applications. RS422 allows longer cable distances (up
to 3300 feet) and provides higher noise immunity.
Consideration 3:
Cable Schematics
Although the network configuration and electrical specification are important, the type of
devices being connected to the D2–DCM are just as important. The exact cable
schematic needed really depends on a combination of all three things. There are a wide
range of possibilities when you consider that all three product families, the DL205,
DL305, and DL405 all offer DirectNET communication capabilities.
Hint: Look at Appendix A to determine a cable possibility. Some of these examples
may need to be combined to design a cable for your application.
NOTE: If you are using the D2–DCM to connect an OptiMation operator interface, you must
order our standard pre-made cable, part number OP–4CBL–2. If you are using a DV–1000,
you must build a custom cable. See the cable diagram at the end of Appendix A.
The following diagram shows the port pinouts for the D2–DCM and the bottom port of the
DL240 CPU. These are the two most likely combinations that you will use. Notice that the
D2–DCM has two sets of RS422 pins. These pins are internally connected and can make
it easier to wire multidrop connections.
D2–DCM Pinouts
RS232C
RS422*
1
RS232 TXD
RS232 RXD
RS232 RTS
RS232 CTS
+5V
0V
D2–240 Bottom Port
1
14
14
2
2
15
15
3
3
16
16
4
4
17
17
5
5
18
6
19
7
20
8
21
9
22
10
23
11
24
12
25
13
+5V
0V
RS422 RTS+
RS422 RTS–
RS422 RTS+
RS422 RTS–
RS422 CTS+
RS422 CTS–
RS422 TXD+
RS422 TXD–
RS422 RXD–
RS422 RXD+
18
6
19
7
20
8
21
9
22
10
23
11
24
12
25
13
RS422 TXD+
RS422 TXD–
RS422 RXD–
RS422 RXD+
* RS422 pins are internally connected
Pin
Port 2 Pinouts
Signal Definition
1
2
3
4
5
6
0V
5V
RS232C DTE RXD
RS232C TXD
Request to Send
0V
1
2
3
4
5
6
Phone Jack
Connector
NOTE: The DL205 CPU ports only support RS232C signal levels. If you are going to have
more than one slave station, you will have to use RS422 and a FA–UNICON RS232 to RS422
converter for each slave station. See the cable diagrams shown in Appendix A for detailed
diagrams.
Data Communications Module, 2nd Edition, 2/03
12
Building the Cable
Consideration 4:
Cable Specifications
Although many types of cables may work for your application, we recommend you
use a cable that is constructed to offer a high degree of noise immunity. A cable
constructed equivalent to Belden 9855 is sufficient. The following specifications are
to be used as a guideline.
Structure . . . . . . . . . . . . . . . . . . . . . . . Shielded, twisted-pair
(RS232C only uses two wires and a ground)
Conductor size . . . . . . . . . . . . . . . . . 24 AWG or larger
Insulation . . . . . . . . . . . . . . . . . . . . . . Polyethylene
Shield . . . . . . . . . . . . . . . . . . . . . . . . . Copper braid or aluminum foil
Impedance . . . . . . . . . . . . . . . . . . . . . 100W @ 1MHz
Capacitance . . . . . . . . . . . . . . . . . . . . 60pf / meter or less
Consideration 5:
Installation
Guidelines
Your company may have guidelines for cable installation. If so, you must check those
before you begin the installation. Here are some general things to consider.
D
Don’t run cable next to larger motors, high current switches, or
transformers. This may cause noise problems.
D
Route the cable through an approved cable housing to minimize the risk
of accidental cable damage. Check local and national codes to choose
the correct method for your application.
D
Consider redundant cabling if the application data is critical. This allows
you to quickly reconnect all stations while the primary cable is being
repaired.
Cable Shield Grounding — It is important to ground the cable shield to minimize
the possibility of noise. The preferred method is to connect one end of the cable
shield to the connector housing. If noise problems are still present and you have a
good earth ground for the cabinet, you must connect one end of the shield to the
cabinet earth ground. Don’t ground both ends of the shield because this will create
induced noise on the cable.
ÎÎÎÎÎ
ÎÎÎÎÎ
ÎÎÎÎÎ
Step 1: Strip back about 2.5” of the shield.
2.5”
Step 2: Crimp a ring connector onto the shield.
Data Communications Module, 2nd Edition, 2/03
Step 3: Secure the shield to
the connector shell.
13
13
Building the Cable
Multi-drop Termination Resistors — It is important you add termination resistors
at each end of the RS422 line. This helps reduce data errors during data
transmission. You must select resistors that match the cable impedance. For
example, a typical 22 AWG solid conductor cable with 4.5 twists per foot has a typical
impedance of about 120 ohm.
There are two ways to actually connect the resistors.
D
Line-to-Line — this method balances the receive data lines (IN+ and
IN–) and requires one resistor at each end of the line. (The cable
diagrams we’ve provided show this method, but you can use either).
D
Line-to-Ground — this method also balances the receive data lines, but
common mode noise rejection is improved significantly. This method
requires two resistors at each end of the line. Also, since there are two
resistors, the sum total of both resistors must match the cable
impedance.
The following diagram illustrates the two options.
Line-to-Line Termination for the D2–DCM
Master
Terminate
at Master
DirectNET
Slaves
120W
Resistor
Slave
Last Slave
7
10
11
12
13
GND
+RTS
–RTS
+CTS
–CTS
7
19
18
11
23
GND
+RTS
–RTS
+CTS
–CTS
14
15
16
17
+OUT
–OUT
–IN
+IN
17
16
15
14
+I
+IN
–IN
–OUT
+OUT
22
23
24
25
+OUT
–OUT
–IN
+IN
22
23
24
25
+OUT
–OUT
–IN
+IN
120W
Resistor
Line-to-Ground Termination for the D2–DCM
Master
Terminate
at Last Slave
Slave
Last Slave
7
10
11
12
13
GND
+RTS
–RTS
+CTS
–CTS
7
19
18
11
23
GND
+RTS
–RTS
+CTS
–CTS
14
15
16
17
+OUT
–OUT
–IN
+IN
9
10
16
14
+IN
–IN
–OUT
+OUT
22
23
24
25
+OUT
–OUT
–IN
+IN
62W
Resistors
62W
Resistors
Data Communications Module, 2nd Edition, 2/03
14
Building the Cable
Network Amplifiers — If you have more than 16 slave stations, you must use an
RS422 amplifier to maintain the signal levels. The best amplifiers are regenerative,
that is, they try to improve signal quality by reducing any noise signals that are
present. (They amplify the signal and not the noise if possible.) Some amplifiers are
not regenerative and amplify the noise as well as the signal. You can purchase
amplifiers from several sources. The Black Box catalog is one of many good places
to start; they sell direct. Call 1–800–555–1212 and ask the 800 directory assistance
operator for their phone number. You can also look for a amplifier supplier on the
internet. One web site to look at is www.idealsolution.com, or search for other RS422
amplifier web sites. The following diagram illustrates some instances where an
amplifier is necessary.
Serial Slave Connection
1-16 Slave Stations
RS422
Amp
Master
Station
Slave
Slave
Slave
Slave
Slave
Parallel Slave Connection
1-16 Slave Stations
RS422
Amp
RS422
Amp
Slave
Master
Station
Slave
Slave
RS422
Amp
Slave
RS422
Amp
Slave
Slave
Slave
RS422
Amp
Slave
RS422
Amp
Slave
Data Communications Module, 2nd Edition, 2/03
Slave
Slave
Slave
15
15
Building the Cable
A Quick Test Cable
AutomationDirect offers a Universal Cable Kit (part number FA–CABKIT). This
cable kit allows you to connect various types of DirectLOGIC products with an
RS232C cable. The kit consists of cable (phone cable with male plugs already
attached) and several specially wired connectors. The special connectors are a
D-sub style with built-in female phone jacks. The kit includes a wide variety of the
special connectors so you can use one kit to connect products from the different
DirectLOGIC family of products. To use the kit with the D2–DCM, just follow these
steps.
1. Plug the appropriate D-sub connector onto the D2–DCM.
2. Plug the appropriate D-sub connector onto the other device you are
connecting to the D2–DCM.
3. Connect the cable to the two D-sub connectors.
WARNING: This cable is suitable for quick testing situations and must not be used in
actual applications. This cable is not shielded and is highly susceptible to electrical
noise. Electrical noise can cause unpredictable operation that may result in a risk of
personal injury or damage to equipment. Use the cable specifications described
earlier in this manual to select a cable suitable for actual applications.
Build A Test Cable In 30 Seconds
1. Attach Universal Cable Adapter to the D2–DCM
2. Attach another Universal Cable Adapter to the
Device which will connect to the D2–DCM
3. Attach the Universal Cable
9 Pin
25 pin
Universal 9 pin
D–sub connector
Universal 25 pin
D–sub connector
Cable Kit Contains one (1) each of:
RJ12 to RJ12
nonĆshielded cable
RJ12 to RJ11
nonĆshielded cable
Phone jack to 9 pin
female D–sub connector
Phone jack to 9 pin
D–sub connector
Phone jack to 15 pin
D–sub connector
Universal 25 pin
D–sub connector
Data Communications Module, 2nd Edition, 2/03
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