24 Apr
2007
24 Apr
'07
10:59 p.m.
Subject: Re: Hand-rolling a CP/M machine
From: Warren Wolfe <wizard at voyager.net>
Date: Tue, 24 Apr 2007 15:36:14 -0400
To: "General Discussion: On-Topic and Off-Topic Posts" <cctalk at
classiccmp.org>
On Tue, 2007-04-24 at 12:01 -0400, Ethan Dicks wrote:
Basically I like to call it this way.
CP/M doesn't care how it gets there, only that it does.
Right. That much I get... so once CP/M is
running, it's ordinary not
to refer to the boot ROMs? There's typically not a requirement to
keep some low-level BIOSy stuff in ROM?
No, there is no requirement to keep ANY ROM available after boot.
It is preferable, in most cases, to have the entire address space made
up of RAM once the system is actually running, as opposed to booting.
Some cases involve copying the ROM contents to RAM during boot, and then
disabling ROM. Again, as has been implied, EVERYBODY chose their own
method -- some were better than others, naturally enough. As a matter
of fact, for those systems which implement ROM at 0000 for booting, the
ROM *MUST* be disabled for any even half-way normal CP/M system to run.
(See the previous discussions on CP/M for Radio Shack Models) Right. I know
that there are *many* CP/M hardware configurations; I
am trying to get down the nub of as minimal a hardware design as
possible.
CPU, 64k RAM, disk(ette) controller, ROM able to be disabled (could
be on controller), serial port. Anything else is gravy.
Sure. For the
minimal system I have in mind, I'm planning on a VT100
or some modern machine running a terminal emulator (Kermit, et al.) to
handle screen formatting.
Perfect. A video card will chew up valuable RAM, and many of
them are only 16x64,
but it does let you do real-time screen updates, games etc.
Ah... now we are onto something - games... are there many games for
CP/M that require a video card, or were most happy with whatever sort
of TTY-type device (ANSI codes or not) was out there? 
25 Apr
25 Apr
8:49 a.m.
On 4/24/07, Allison <ajp166 at bellatlantic.net> wrote:
I'd simplify diskette controller to mass storage
(any form).
I had more of a solid-state 'disk' in mind, anyway (SD, CF, etc.) If
I'm going to twiddle floppies, I'll just fire up a Kaypro. I might
also consider a TU58 emulator running from a modern PC, attached via
the B-channel of a Z8530 SIO. This exercise is more about the Z-80
and CP/M than about designing/implementing a floppy controller.
>> > A video card will chew up valuable RAM,
and many of them are only 16x64,
>> > but it does let you do real-time screen updates, games etc.
the logic for rolling your own VDM1 equivalent is 1K
of ram in the
address space and a screen refresh (H and V timing, line counters)
are about 10 or so TTL pieces. It's actually simple if you do not
have to build a S100 bus interface.
If that's the case, I'd probably consider a 6845 - I'm familiar with
the chip from the 8032 PET, and I know they aren't hard to find. For
now, though, I'm still going to stick with a UART and terminal.
You can copy the screen logic for TRS80 as that is a
basic 64x16 as well.
Good thing to keep in mind.
-ethan
8:24 p.m.
You can copy
the screen logic for TRS80 as that is a basic 64x16 as well.
Good thing to keep in
mind.
7:40 p.m.
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?
-ethan
You can copy the screen logic for TRS80 as that is a
basic 64x16 as well.
Good thing to keep in mind. 
10:23 p.m.
Ethan Dicks wrote:
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?
That works but to find the PROM data you have to look at some very old
memory data books. I have yet to find any nice 8x11? fonts that fit
in a 9x12 character block could be copied.
-ethan
7:49 p.m.
On 25 Apr 2007 at 13:24, woodelf 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.
At the expense of getting booed off the topic, if you need simple
80x24 and are using something like an 8085, the 8275/8276 CRT
controller with an 8257 DMA controller (in auto-initialize mode)
doesn't take a lot of extra glue. The gotcha is that "special
effects" like bolding and underlining take up space on the display
(Doesn't the Wyse 50 do that?). There is a "transparent" mode, but
management of the screen buffer becomes a real headache. I've never
tried to interface an 8257 to a Z80, so I don't know if the timing
works there.
Cheers,
Chuck
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days inactive
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