DCE RS232 on PDB to Serial (RS232 DCE) Printer, Null Modem Cable needed?

WBA Consulting

So I have been struggling with getting an Eltron serial printer to work properly with a BS2 on a PDB. I am using the RS232 circuit on the PDB which is setup as a DCE. My connections are setup properly, but I had to modify a serial cable and swap pins 2 and 3 (TX/RX) to get it to work. After spending more time reviewing the RS232 spec, the PDB Rev C Schematic, and my layout, I came to the following conclusion:

To connect a DCE Serial device to the DCE Serial port on the PDB, a null modem cable is required.

Any other RS232 Serial experts agree/disagree with this conclusion? I am considering building my own max232 circuit on the PDB that is wired as DTE, just to eliminate the confusion and use a standard serial cable.

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Andrew Williams
WBA Consulting
IT / Web / PCB / Audio

stamptrol

Andrew,

After many years of using it, I have come to the realization that RS-232 is an extremely flexible but highly variable standard.

You've just gone through the usual exercises in most every '232 installation.

I usually start out by hoping a standard cable ( M-F, straight through) will physically connect the two devices. If it will, then the only issue is knowing whether it should be 2 - 3 or 2 - 2 to match the Tx and RX from the two devices. The other thing that can frustrate you is the handshaking required by some devices which many times require a 4-5 or 6-8 jumper.

As to wiring your PDB to be DTE, if it always was going to be the Data Terminal Equipment, then that would make sense. But, in many applications, the PDB would be the Data Communication Equipment and now you're non-standard again. All depends on the point of view and purpose of the equipment involved.

I just keep a bunch of gender changers and null modem converters around to use during set up. When everything works, I build a dedicated serial cable and make a note in the shop logbook.

Cheers,

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Tom Sisk

http://www.siskconsult.com
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WBA Consulting

Tom, thanks for clarifying my guesses. I think I am on the right track now. The DTE circuit won't be from re-wiring the one on the PDB, but will be a new one that I will make on the breadboard with a DIP max232. I may make it on a piece of perfboard to make it modular. My project using the serial connection will only work as DTE. A BS2 will control a Symbol LS1220 barcode scanner and use the data to print formatted labels on an Eltron (or Zebra) printer using EPL (or ZPL) language through a serial connection.

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Andrew Williams
WBA Consulting
IT / Web / PCB / Audio

stamptrol

That should work well for you. I've done numerous systems with barcode scanners and Epson and Zebra serial printers.

On one, I did have to move up to a BS2sx for both higher data speed and the ability to have some extra scratchpad memory available when reading long character sequences.

Cheers,

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Tom Sisk

http://www.siskconsult.com
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