Problem with Parallel Printer under Cromix

[grahamlees1]

Hi Folks,

I'm trying to get a PC style printer to operate with a TUART parallel port under Cromix Plus 162.  I have the TUART setup as per TUART #1 in the Cromix Plus Admin Manual and i have regenerated the OS with a parallel printer on the TUART. 

I did find a spreadsheet with the pin mappings for CDOS by Martin Eberhard (although i can't for the life of me remember where i found it) from the TUART to a "normal" PC style cable.  I made up an adapter cable and it works fine with CDOS.  Excellent!

When i tried with Cromix Plus 162 i found that everything goes well for a single character.  After that it doesn't go at all.  No characters are emitted and the process (in my case ls >/dev/lpt1) stops dead until i terminate it with a ^C.

The single character is correct ("b") and i can see with the scope (see attached STRB_L, BUSY/READY_L, ACK_L) that the printer responds to STRB_L by asserting BUSY and then negating BUSY while producing an ACK_L pulse.  The status lines from the printer look fine. (i use _L for active low btw)

I know the printer is not hung up because if i shutdown cromix and go to RDOS i can bit bash the output port (54h) to send more characters.

The various status inputs and ACK_L from the printer are connected to input port pins on the TUART.  The TUART manual leaves the pin assignments up to the OS so Cromix could be different to CDOS.   I've tried a few variations but the result is always the same.  eg I routed ACK_L to SENS_L.

I expect the Cromix driver is waiting for something - just not sure what!  

Any thoughts? 

Graham

[Mike Arnold]

Graham

I think that this is to do with interrupts (CDOS is obviously polled). Try looking at pin 15 as I believe that this is the ack strobe back from the printer. I think what you need is in the PRI manual under the 3703 wiring. Later PRI not earlier one. Can't remember what we did in the day but definitely had standard parallel printers (eg Anadex) running from Cromix.

Mike

[grahamlees1]

Thanks Mike,

I currently have ACK_L fed into SENS_L (Pin 15) but without success.  Actually i've tried feeding ACK_L into each of the spare inputs.  It is possible that there's a board fault but it's the same on the second port and the serial ports work fine.  

Graham

[Mike Arnold]

Graham

You got me curious so I booted my Cromix system up and checked that it printed to my Epson and all OK. So I attach the cable wiring for you. If your printer does not use a standard Centronics connector then you will need to modify it. I also attach a photo of the TUART with switch settings. 

Mike

[Mike Arnold]

And at the risk of teaching grandmother to suck eggs, as they say... is your interrupt priority cable installed correctly? For some reason the pins on the FDC and TUART are reversed so I have connected it the wrong way round in the past.

[grahamlees1]

Thank you Mike,

I came back to this after a few days and in the the intervening period i seem to have developed the skill to count to 15 correctly.  More an issue of egg on face than sucking eggs.  It is now printing! 

It even prints from Wordstar.  Very happy.

Graham