🚀 go-pugleaf

In article <1992Dec8.035415.26358@grebyn.com>, malak@grebyn.com (Michael Malak) writes:
> What is the best way to achieve background printing in a DOS program, to
> the level that Word Perfect achieves it?  Is it using IRQ7?  I've tried
> guessing at how to use IRQ7 with no luck.  As far as I know I'm enabling
> the 8259 _and_ the interrupt enable bit at the LPT1 port address, but I
> don't get an interrupt when I send a character to the printer via INT
> 17H.  Any suggestions?  Any example source?


I don't know how many times this needs to be explained... maybe
this should be thrown into the FAQ:  Never ever ever ever mix
code that directly touches add-on chips AND also calls related
BIOS functions.  BIOS makes too many assumptions.  Don't trust
BIOS to do what you would like it to do.  If you take the time
to talk directly to hardware, then don't cut a 5 minute corner
by calling BIOS and ending up with an erroneous program.  The
only cool BIOS tricks are to use it to switch to some operational
mode and back (say video mode 13H, or setting all basic serial
parameters). Other than that, use either _only_ BIOS or _only_
direct programming.

Now Michael, in your case the problem is simple. INT 17H on most BIOS's
simply rewrites the command-byte to send the line signals to the
printer, thus it also disables the IRQ of the port. The only way out
is to design your own character output routine and not use INT 17H.

Aki.
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