Hi,
I replaced a PC on one of our machines yesterday. The existing PC had 2 RS232 ports on a half-height expansion card. The ports were connected to two RS232-422 converters, which were in turn connected to a motion controller, and a CP341 Siemens S7-300 PtP unit. Comms were working fine.
I replaced the PC for a new (Win 7) unit with a USB-RS232 adaptor with two ports. I connected the two devices. The communications with the motion controller was just fine, worked first time with no problems.
I could not get the comms to the CP341 at all. I tried changing a setting on the RS232-422 converter for RTS from "auto" to "RTS" but this made no difference.
The COM ports were correctly addressed and I had previously verified both ports by connecting a null modem cable to them and talking on both ports and receiving a reply.
Because of time pressures, I did not make any other attempts to debug the problem. Since the PC had one on-board com port, I decided to use this. I reconfigured the software to use Com1 instead of Com5, and it worked first time.
The RS232-422 converters should have been a constant and in my experience RS232 is less finicky than RS422 with differences in voltage levels etc.
What could the problem have been that it worked with one device and not the other, but resolved by using a "real" serial port?
thanks
Martin
I replaced a PC on one of our machines yesterday. The existing PC had 2 RS232 ports on a half-height expansion card. The ports were connected to two RS232-422 converters, which were in turn connected to a motion controller, and a CP341 Siemens S7-300 PtP unit. Comms were working fine.
I replaced the PC for a new (Win 7) unit with a USB-RS232 adaptor with two ports. I connected the two devices. The communications with the motion controller was just fine, worked first time with no problems.
I could not get the comms to the CP341 at all. I tried changing a setting on the RS232-422 converter for RTS from "auto" to "RTS" but this made no difference.
The COM ports were correctly addressed and I had previously verified both ports by connecting a null modem cable to them and talking on both ports and receiving a reply.
Because of time pressures, I did not make any other attempts to debug the problem. Since the PC had one on-board com port, I decided to use this. I reconfigured the software to use Com1 instead of Com5, and it worked first time.
The RS232-422 converters should have been a constant and in my experience RS232 is less finicky than RS422 with differences in voltage levels etc.
What could the problem have been that it worked with one device and not the other, but resolved by using a "real" serial port?
thanks
Martin
