Date   : Fri, 06 Jul 1984 05:40:54-PDT (Fri)
From   : hplabs!sdcrdcf!sdcsvax!akgua!mcnc!ncsu!uvacs!edison!jwc@Ucb-Vax.arpa
Subject: Re: MODEM730 & KAYPRO: can't print to Epson

Steve, the trouble you're having is due to a bug in the Kaypro BIOS and ROM.
According to the DRI manuals, BIOS call 14 (LISTST) should return a zero in A
if the printer is ready, and an FF if it is not. Kaypro sets the zero FLAG,
but does not return a zero. Their LIST call checks the flag, so it works fine
for them. But MODEM7 et al checks for the contents of A, not the zero flag.
       There are two fixes:
1) Patch MDM7xx to get rid of the ANA A which sets the flag after the call to
the BIOS.
or
2) Patch the BIOS. This is about a six-byte patch, replacing the BIOS jump
vector with a jump to a free area, which contains:
                       CALL LISTST
               RNZ
               XRA A
               RET.
If you have access to Compuserve, there's a complete patch in CP-MIG XA1.
I understand it is also on the Detroit TRCM.