I figured it out! It involved using the AWA and ARl instructions rather than the ARD and AWT instruction. The only quesiton is: why couldn't I use the ARD or AWT instructions? I used the proper CR termination?
The AWA and ARL commands Write and Read only a specifed number of characters from or to the RS232 buffer, with the number entered in the instruction box. I would guess that in your earlier tries, you were writing more characters than the two-character+CR chiller commands, and trying to read the entire buffer instead of the 7-character response from the chiller. That is why early in this thread, I asked you WHAT was being written from string ST9:0
I knew that if ST9:0 conatained more characters than the specificed chiller command line, you would get zilch in return.
You can use the other earlier commands, if you make sure you are writing and reading the number of characters with proper CR, as used by the chiller program.
I was messing around using the hex conversion for the RS[CR] command. I changed it back to RS[CR] and now reads 6 characters. I also tried it without the brackets or RSCR.
This was my response to the question regarding ST9:0 in other words the 12 characters was me trying a hex conversion which of course didn't work. I did try it with RSCR and it did not reply.
I had my number of characters set to 0 which, according to the instructions means it should read what ever is in the buffer. Or is this not correct?
Yes, but the PLC RS232 buffer can contain many more characters, everything that has been sent after it was last cleared. If you use the commands that read or write the entire buffer, then you have to control what is in the buffer, not just in one line or in a string up to the next CR character. To control what is in the buffer, you have to "handshake" with it using one of the control bits, such as R6:0/DN or similar.
