Model II Graphics Card Installation
GrantH
TRS-80. It comes with the card, 2 ribbon cables with card-edge
connectors which terminate w/IC plug-ins, obviously to replace IC's on
the normal video card. The documentation includes only discussing
grahics BASIC, programming in other languages, etc. There's a bit
about having my qualified Radio Shack technician install the card, no
instructions on the installation.
Wondering if anyone knew the hardware installation step?
Grant
Mike Y
"GrantH" <gr...@ghhsoftware.com> wrote in message
news:e859639c-51c8-4d98...@d1g2000hsg.googlegroups.com...
OK, I HOPE I remember this right...
What you do is open the card cage (power off, of course! And make sure
you discharge yourself as well!) and remove the video card. You will remove
the video card. You will careful remove the 6845 chip and the ROM
chip from your video card, and move them to the graphics card. Then you
will plug in the cables that came with the graphics card into the sockets
where you removed the 6845 and the ROM, and carefully route the cables
to the graphics card. Be careful of pin '1'!
Put the video card back into the card cage with the graphics card in the
adjacent slot.
Do NOT leave any empty slots between cards in a Model II card cage, as
not all signals are 'in parallel'. The interrupt enable signal 'daisy
chains' through
cards, and even if a card doesn't use the signal (like the memory card) it
still passes the signal through.
If the machine video works as normal when you power back up, you have it
working correctly.
The graphics card works by intercepting the video address signals and doing
an XOR of the character data with the graphics data. With the graphics all
set to '0', then the screen looks normal. Any area that sets graphics '1'
bits
will be inverted. That is, black becomes white and white becomes back.
If you get noise and tearing of graphics, then the LS chips that drive the
address lines to the RAM on the graphics board need replaced with S parts.
(LS technically could drive 10 standard loads, but there were 16 RAM
chips. Most boards worked, but some needed changed.) I think the
boards were all changed in production but a few might have gotten out with
LS parts.
Mike
GrantH
Thanks - I'll let you know - could be a little while before I can get
to it - but thanks for the feeback (never would have figured that out
on my own!).
Grant
Mike Y
there was
a 'twist' in the cable to make sure pin 1 stayed pin 1. Well, not a twist,
but
a loopback.
But then, that may only have been on the early prototypes.