Modbus configuration
Modbus Parameters relating to transmission
At a Glance
Transmission
Speed
Delay between characters
After configuring the communication channel, you need to enter the transmission parameters.
These are split into six windows: l l l l l the Transmission speed window, the Delay between characters window, the windows specific to Data and Stop, the Parity window, the RTS/CTS delay window.
The window looks like this:
Transmission Speed
9600 Bits/s
This window is used to select the transmission speed of the Modbus protocol used l l l by the module, and is compliant with the other devices: the default speed is 9600 bits/s, the other speeds available are 1200, 2400, 9600 and 19200 bits/s, speeds of 300 and 600 bits/s are only available with the PCMCIA card TSX SCP
111.
The window looks like this:
Delay between characters
Default 4 ms
This is the end delimiter detection delay plus the maximum time between two characters received. It is managed when the PLC is receiving messages, whether it be a master or slave.
You are advised to use the default values on configurations that do not have a modem or other intermediary device. Otherwise, you must use higher values.
Note: The default value depends on the transmission speed selected.
Note: There is one restriction on the 'Delay between characters' value on channel
0 of TSX SCY 11601/21600/21601 modules (see table below).
TLX DS COM PL7 xxE
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Modbus configuration
The table below gives the maximum values of the delay between characters depending on the transmission speed:
Speed (bits/s)
1200
2400
4800
9600
19200
Max. delay between characters (ms)
212
106
53
26
13
23
23
22
Max. delay between characters
(number of characters)
23
23
Data
Stop
The window looks like this:
Data
ASCII (7 bits)
RTU (8 bits)
The Data field can be used to enter the type of coding used for Modbus communication. This field is to be configured as a function of the other devices: l RTU mode: l the characters are coded on 8 bits, l the start and end of frame delimiters are detected by a silence of 3.5 characters, l l l l frame integrity is checked using the CRC checksum contained in the frame.
ASCII mode: the characters are coded on 7 bits, the start delimiter is detected by receiving the characters ":" or by a silence longer than the delay between characters.
The end delimiter is detected by a CR and LF (carriage return and line feed) or by a silence longer than the delay between characters.
Note: The value 1000 in ASCII mode corresponds to an infinite delay between characters.
The window looks like this:
Stop
1 bit
2 bits
The Stop field is used to enter the number of stop bits used to communicate on
Modbus. The possible values are 1 or 2 stop bits. This field is to be configured as a function of the other devices.
Note: The default value is 1 stop bit.
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TLX DS COM PL7 xxE
Parity
Modbus configuration
The window looks like this:
Parity
Even Odd None
This field is used to define whether or not a parity bit is to be added, and, if so , what its type will be. The possible values are Even, Odd or none (Even by default). This field is to be configured as a function of the other devices.
RTS / CTS Delay The window looks like this:
RTS / CTS Delay
1 X100 ms
Data Carrier
(DCD)
Before sending a character string, the module activates the RTS (Request To Send) signal and waits for the CTS (Clear To Send) signal to be activated.
This allows you to enter: l the maximum waiting time between the two signals. If this time expires, the request is not sent to the bus. l l the value is expressed in hundredths of milliseconds, the default value is 0 ms, l l l the value must be between 0 s and 10 s, the value 0 specifies that there is no management of the delay between the two signals.
carrier management (DCD signal, Data Carrier Detected) is only used when communicating with a controlled carrier modem: l l if this option is selected, characters can only be received if the DCD carrier signal has been detected, if this option is not selected, all characters received are taken into account.
TLX DS COM PL7 xxE
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Modbus configuration
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TLX DS COM PL7 xxE
