Re: xx-DOS (im)possible problem!

Hi Eric,

The real problem is with Clipper programs that use the isprinter()
command. I had information on it's source and it calls int 17 with
ah=02 and tests if the returned value is 90h.
I cannot change the programs: I only have to make them work :(

I made a small C test program. and tested it in many ways:
- local printer: ok
- no printer: ok (returns 90h but I have experience that this he dependent
- dos-box in win98: ok (local printer, no printer and network printer)

As to the ack pin: yes it is a 10us pulse and normaly stays high
and is read as 0 by the bios. ( I made printers, that side I know)

The big questions are:
1) how does it work with ms-dos 7.10 and not ms-dos 6.22/Freedos?
2) would it be ok it I just turn that bit off with a tsr?

thanks for any help, anyone,
Alain

> Hi, INT 0x17 is indeed NOT normally handled by DOS. However,
> as you use network printing, the network driver probably tries
> to redirect it. But it would be better to use the PRN or LPT1
> device instead of INT 0x17 to access network-redirected printers.
> 
> It is possible that the MS-Client driver does not at all modify
> INT 0x17 and what you get is the status of the local printer port
> instead (try to connect a printer, put the local printer in online/
> offline/error states...). Windows DOES modify INT 0x17 in the DOS box
> because it wants to capture DOS printing data and redirect it to the
> Windows queue, to avoid that DOS programs mess with the printer
> directly (AFAIK).
> 
> INT 17 - PRINTER - GET STATUS
>         AH = 02h
>         DX = printer number (00h-02h)
> Return: AH = printer status (see #00631)
> 
> Bitfields for printer status:
> Bit(s)  Description     (Table 00631)
>  7      not busy
>  6      acknowledge
>  5      out of paper
>  4      selected
>  3      I/O error
>  2-1    unused
>  0      timeout
> Notes:  If both, bit 5 "out of paper" and 4 "selected" are set, the MS-DOS/
>           PC DOS kernel assumes that no printer is attached.
> 
> ACK is - I think - only a bit that flashes for a moment when the printer
> tells you that it successfully received the data. With no printer attached,
> it is probably stuck to a different value than the idle state of an attached
> printer would be. While the timeout bit comes from the BIOS, most other bits
> are just what you see at some I/O port, partially inverted by the BIOS.
> 
> Eric