25 Apr
2007
25 Apr
'07
9 p.m.
Subject: Re: Hand-rolling a CP/M machine
From: "Ethan Dicks" <ethan.dicks at gmail.com>
Date: Wed, 25 Apr 2007 14:40:08 -0400
To: "General Discussion: On-Topic and Off-Topic Posts" <cctalk at
classiccmp.org>
On 4/25/07, woodelf <bfranchuk at jetnet.ab.ca> wrote:
Well if anybody is doing VDM-1's the big problem is that you can't find
the Character ROM any more. I like the idea of TTL display like VDM-1
but since this is not the late 70's a 80x24 screen is reasonable
and the data out is a simple VGA format, since the monitors are easy to
come by.
As in the old Chargen ROMs like on this board?
http://www.classiccmp.org/dunfield/d/h/tvt.jpg
(I have one that I bought new and has yet to be attached to a KIM-1).
With as fast as CMOS ROMs are today, why not use a 27C64 and burn your
own charset to it? It's not tough to do, but is there a technical
reason it wouldn't work?
It works very well and it's easy to find a pattern like 2513 (5x7) or
a 6674 (7x9) and burn an Eprom. Compared to the parts of that day
even 2716 is both big enough and plenty fast. I like to use 27C64s
as I have a bunch of pulls and it's no big deal building up a pattern
as a copy or custom.
FYI: to do it by hand all one needs is a sheet or a few of grid paper
and a #2 graphite thingie. The order you enter the data is row for
the low address lines (usualy 4 address lines) and the high address
lines are the ascii value (0-127) that corosponds with the char.
Allison
You can copy the screen logic for TRS80 as that is a
basic 64x16 as well.
Good thing to keep in mind. 