serial com works on one pc, not others

[andy pluister]

I have a scale indicator that communicates via RS-485.
I purchased an RS-485/RS-232 converter that plugs into the com
port on the PC. I wrote a simple program that opens com1, sends
the appropriate command to prompt the scale indicator for the
weight, and then reads the weight from the buffer.

This program has run fine on my PC for a year. Now, I need to
move the hardware to another PC in our office, but I can't get
it to work! I've tried two other PC's and had no luck on either
one. I am using the OPEN "COM1: 9600,N,8,1,RS,CD,CS" AS #1
command to open the serial port. I have the serial port settings
under Win2000 set up the same for all three PC's with no flow
control. The working PC is a Compaq 750MHz Pentium II and the
two non-working PC's are 350 MHz Pentium Compaq's.

Does anyone have any ideas that I could try???

[Mel Bishop]

Just right off the top of my head:

If the box(s) you are moving to have internal modems, the modems
could be set to COM1. That would leave the serial port on the
back of the box set to COM2. Check the CMOS on boot-up to make
sure the IRQ's and other stuff are what you expect them to be.

One other thing: You can try changing
OPEN "COM1: 9600,N,8,1,RS,CD,CS" AS #1
to
OPEN "COM1: 9600,N,8,1,RS,CD,CS,DS" AS #1

Adding the DS may make a difference, it may not.


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[Tom Hanlin]

Check the BIOS setup to make sure the comm ports are enabled.

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Tom Hanlin
PowerBASIC Staff

[Aldo Cavini]

Andy,

the RS-485 communication is half-duplex: the RS232-RS485 converter switches the communication from TX to RX and vice-versa. The TX/RX switch can be accomplished (from the top of my head) two ways: verifying the RS232 TX activity (RS485 will TX while the RS232 TX is active) or verifying another line status. Some converters I used some years ago used the RTS line (request to send: it is active prior and during the TX activity).

If Mel and Tom ideas didn't solve the problem, try removing the RS option from the OPEN statement. Furthermore, try removing the CS option - in this case, you must hardware connect the RTS and CTS lines toghether (may be the RS232-RS485 converter connects the two lines itself).

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[This message has been edited by Aldo Cavini (edited July 18, 2002).]