Serial Printer Question
8 messages in this thread
Serial Printer question:
Which data lines are used by a SERIAL printer to signal "Online",
"Offline" and "Paper out/Printer Off"?
I am using the printer.device PRD_QUERY command to determine whether my
program can print or not. I have the code for a parallel printer working
fine, but I'm not familiar with serial printers (but I do want my program
to support them naturally).
Thanks for your help.
David Czaya …via AutoPilot
73445,407
Go to Radio Shack, buy the $15 serial port tester. It will show you the names
associated with each serial line (DSR, DTR, etc.). It has little LEDs that
light when the line is active. The answer to your question is, "It depends."
It depends on the cable and the devices between them. Some serial devices
ignore the lines that other devices might use to indicate those states.
Understood. What is the typical way of handling these functions then? All
I want to do is be able to detect an online/offline condition. If the
printer is parallel, it's no problem, how do software writers handle
serial printers? Do they simply ignore the conditions?
David Czaya …via AutoPilot
73445,407
I'd think that serial printers would probably assert DTR or DSR, depending on
how they were wired, when they were online. I seem to remember some printers
that were wired as if they were terminals, and others as if they were computers
themselves. (The equivalent of needing a null modem cable.)
Offhand, I'd say the printer.device should handle this. The serial chip
interface must show the state of readiness.
Correct, most serial printers use DTR DSR, (7 Wire cable). There are
however some that use Xon and Xoff (three wire cable)
As to whether you need a null modem connection or not, it could be either
way. It just depends on how they decided to do it.
Bob Comer — Cruising the nets on Autopilot!
Cheyenne, Wyoming U.S.A.
That's why I told him to search the printer.device functionality for this…
it's the insulation from the XON / XOFF, DSR / DTR level of "online" detection.
XON / XOFF printers are pretty rare, I think – I can only remember the DEC
LA50.
>> That's why I told him to search the printer.device functionality for
>> this… it's the insulation from the XON / XOFF, DSR / DTR level of
>> "online" detection.
Allowing the printer device to time out and put up an alert is one way, I
guess. For the parallel printers, I can do a PRD_QUERY and know
immediately whether the printer is online or not. For serial printers, all
the data lines are available to read, but without knowing how the printer
is cabled, I guess I'll have to default to a timeout.
Ok, thanks a LOT for your help. It is greatly appreciated.
David Czaya …via AutoPilot
73445,407
I had one at my last job… (Don't remeber the brand…) Terrible
printer, but the speed was pretty decent.
Bob Comer — Cruising the nets on Autopilot!
Cheyenne, Wyoming U.S.A.