Hand-rolling a CP/M machine

[Allison]

>
>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:
>> >> You can copy the screen logic for TRS80 as that is a basic 64x16 as well.
>> > Good thing to keep in mind.
>>
>> 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