RS 485

[David Clarek]

I have a Baldor Servo Drive with a RS485 communications port.  The pins on the port are marked Ground, TXA and TXB.  The terminal on the T100MD+1616 are marked - and +.  What is the proper hook up.  Also, I have set the Address for the Baldor to (1) how do  I set up my communications.  Please give me an example of a session where I would send the string "v1000" to the baldor and recieve an 8 bit number.  I am new to 485 and need some assistance.

Thanks Dave

[support]

You can connect TXB to the RS485 "+" terminal and TXA to the RS485 "-" terminal.

Next you need to setup either the PLC or the Baldor to talk at the same baud rate and format. The default on the PLC is 38,400, 8, 1, n. If the Baldor has a different baud rate you may want to change that to the PLC's standard baud rate and format. Otherwise you can use the PLC's SETBAUD command to change the PLC's baud rate and comm format to that of the Baldor.

For the PLC to send a string "v1000"  (I hope you mean ASCII strings, not binary number), execute the following statement:

PRINT #3 "v1000";

We assume that there is no need to send "CR" character to terminate the string? Otherwise you should remove the semi-colon at the end of the statement to force it to send CR character.

What format is the 8 bit number that you will receive? Is it binary number? If so, use the:

   X = INCOMM(3)

to read binary data from the RS485 port. You can poll it until X become non -1.

[D Clarke]

Thanks but

I thought that RS485 was a multi drop connection and that the device address number (The Baldor device ID was set to 1) was needed.  Does this not apply to a single connection.  By sending just a "print #3" , how does my Baldor know that it is being addressed?  Is there some setup procedure?

Thanks Dave

[support]

That will depend on what the Baldor protocol requires.  If it does not require you to specify the address in the one-to-one connection then you don't have to do it.  We just described to you the command in TBASIC based on what you mentioned in your original posting. I don't know what is the Baldor's protocol  requirement and whether they are to be in binary or ASCII. But whatever it is the TBASIC command should be powerful enough to send out the required command data and receive a response data from your device.