Re: Several answers (3)

From: Andre Fachat (
Date: 1998-04-01 10:17:22 wrote:
> Question: is it possible to send me the SCH of your (final) version of the IEEE 
> interface for the LPT-port?

Uhm. Sorry, I have not (yet) finished this. I have all parts and 
I have the schematics but not yet resoldered the board to the new Sch.
So the new Sch would not be tested, but if you still like I can send 
them to you.

> > After all by switching the _charrom_ to graphics mode....
> How this is done on the PET? I found out by poking 59468,12. but that 
> (certainly) is not the friendly way to do it.
As far as I know (probably PETdoc or pet-FAQ prove me wrong) this is the
only way. Probably there is a PRINT CHR$(??) as in the C64.

> I disagree. 128 ASCII characters PLUS 128 graphic-characters makes 256. Double 
> it for inverting makes 512. 512 * 8 = 4096 = 6332.
> So only ASCII + invert = 6316.

Do don't need to double it for inverting! The 7th bit of the byte read
from memory does not go to the charrom but directly to an exclusive-or
with the shiftregister output that generates the pixel stream!
So you have only 7 address bits for the charset, plus 1 bit for text/graphic
and 1 bit for us/nationalized, plus 3 bit for the rasterline number,
gives 12 bits that make 4kByte to fit in a 6332 _with_ the nationalized charset.

> > But setting it on the nationalized one could probably switch between
> > us and nationalized charsets (as the DIN key does in german C128 machines).
> I do have a German C128 as well. (They were much  much cheaper then here in the 
> Netherlands) And the CHARROM is a 2764 = 8KB in my case!

The C64/C128 doesn't have the hardware inverter, so you have to double the
size of the charrom. Makes 4k for 256 chars * 2 (text/graphics) * 8 (bytes/
char) is 4k for the C64, and *2 for the nationalized charset in the C128
makes it 8k.

hope it helps

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Andre Fachat, Institute of physics, Technische Universität Chemnitz, FRG

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