Date   : Fri, 07 Dec 1990 16:19:54 GMT
From   : olivea!samsung!noose.ecn.purdue.edu!ea.ecn.purdue.edu!wieland@apple.com (Jeffrey J Wieland)
Subject: INTTERM - Problems on my KP2-84

In article <6131@crash.cts.com> mwilson@crash.cts.com (Marc Wilson) writes:
>In article <1990Dec5.155950.22108@ico.isc.com> mikeod@ico.isc.com (Mike
O'Donnel) writes:
>
>>2.  Why does it relocate handlers into different areas
>>    of memory and could this possibly be stomping on
>>    something.  
>
>     It moves itself above 8000h because it needs the ROM in order to
>talk to the screen.  The ROM comes in at 0h-8000h.  If an interrupt
>occurred while the program had the ROM enabled, the interrupt vector
>would point to a random location in the ROM, not in the program.
>Result:  BLOOOIE!

Also, in order for intterm to run on an '83 series Kaypro II or IV, it
has to relocate itself above where the video RAM gets bank switched in.
I believe that the video RAM is mapped in just above the ROM.  Jumping
into the middle of VRAM wouldn't be too healthy, either.  The '84's
use a 6845 video controller, and talk to it through the Z80 IO ports,
the video RAM is not memory mapped.  The '84's have all sorts of
snazzy video attributes, but their video is much slower than the '83's.

On the '83's, people have even bypassed the ROM and used the Z80 block
move instruction to update the screen to make it even faster (like a lot
of PC programs do).  Of course, this makes the programs non-portable.
On the '84's, it should be possible to talk to the 6845 directly to
speed things up.  The BackGrounder II screen driver for the '84's does
just this.  It redraws the Kaypro's screen faster than anything else
I've seen.

>
>>3.  Does anyone have a memory layout and tech. info for
>>    the KPII-84 that they would send me?
>
>     Yes.

MicroCornucopia has a schematic and theory of operation for the '84's
(and '83's and the 10's also).  It's interesting to get even just to
read through and say: "Oh -- So THAT'S why it works that way!"
I'd give you MicroC's address if I had it here at work.  Email me
if you want to get it from them -- I'll get their address for you.
--
                           Jeff Wieland
                       wieland@acn.purdue.edu