RS232 No Rx Data?

[Stephen1234]

I am using a T40H TriPLC and I have a problem regarding RS232 comms.
I have downloaded the VB RS232 comms device manager and can use commands like RI00*, RI01* and WO00FF and I get the expected response without any problems
?however when I send the same command string, say RI00*, via my serial device manager, I don?t get a response from the PLC ? nothing is sent back to the PC.
I?ve listened in to the comms via hyper terminal and I?m definitely sending the same command strings.
The only PLC response I can received with my serial device manager program is the Ctrl-E (0x05) echo.

Can anybody help please?

[support]

The point-to-point command handshaking requires that you send the Ctrl-E, wait for the Ctrl-E from the PLC and then send the command string and these has to be done in a short time. i.e. If a H-series PLC don't see the comand string within some milliseconds after it respond to a Ctrl-E, it will assume that no command is forthcoming and it will then abort the host link command handler.

Your serial device manager may not be programmed to handle the protocol this way. It may be easier to just use the multi-point format and append the ID. If computing the FCS is a problem, then just use the wildcard FCS "00". So let say the PLC ID is 01, send:

   @01RI0000*

The "00*" is the FCS and terminating character. You should get a response on your serial device manager.

[Stephen1234]

Thanks for the reply!

I am now able to communicate point-point using commands like?
@01RI0000*
@01WO00FF00* etc
?without any problems, and I don?t have to worry about the CTRL-E (0x05).

?however, I still need to read the PLC ID so I can use the @??. I don?t want to rely on pre-programming the ID in-house.

Therefore I am sending the following commands; where command 2 is sent immediately after I get the Rx from command 1

1st Command
Tx : <ENQ>*<CR>
Rx : <ENQ>

2nd Command
Tx : IR*<CR>
Rx : ER*<CR>

?as you can see, the command 2 Rx is indicating an error ? I don?t get ER* using VBsample!

Thanks for your help.

p.s. I have also tried command 2 Tx as
IR00*<CR>,
<ENQ>IR*<CR> and
<ENQ>IR00*<CR>
?without any luck

[support]

When you send the Ctrl-E character, don't send the "*" and <CR>. Wait for the Ctrl-E that the T40H-Relay send to you, then immediately send out the "IR*"+<CR> and wait for the response from the PLC. You should study how the VBsample program works and you can have a better understanding.