Short question: Why does it not work to jumper the DTR and DSR pins on the serial port in order to bypass the Rs232 handshaking on an E3645A power supply?
Now the long explanation if anyone has the time:
I am working on an application where I need to establish serial communications between a E3645A Power Supply and a PLC. This PLC has a Rs232 comm port available that I can easily use to transmit and receive ascii strings but has no handshaking/flow control capability. Only Tx, Rx, and Gnd (pins 2,3,& 5). I have verified with Windows hyperterminal that it is sending and receiving strings perfectly.
It transmits commands and communicates fine with the power supply unless I send any query command which requires a response. I get no response and if I send another query command I get an error having to do with an interrupted response/uncleared buffer. If I connect the power supply to a windows PC using hyperterminal and a cable which uses only pins 2, 3, 5 it does the same thing. If I add pins 4 and 6 (DTR & DSR) to the cable (crossed-over) it responds properly to queries. Pins 1,7,8, and 9 can remain disconnected and it will communicate back & forth fine with hyperterminal.
After a quick google search I discovered the easy solution would be to jumper pins 4 and 6 to "fake out" the handshaking but this does not work. Anyone know why?
Thanks in advance
Scott
I figured out how to get around the handshaking so I thought I'd report back in case anybody else ran into this.
Through trial & error I found that if you hold Pin 6 (DSR) high all the time it will respond to query instructions just fine.
Simply jumping it to Pin 4 (DTR) like they tell you all over the internet WILL NOT work with these power supplies because the DTR goes low and stays there while it's looking for a high signal on the DSR.
There is no constantly high signal on the serial DB9 to jump to so luckily the PLC I'm using to communicate had an available 5V supply. Problem solved.