OT: is there such a thing as a modern 6845 equivilent
Russell Davis
know.
i'm a bit bored at the moment and looking for a project to stretch
myself a bit so decided to investigate building a z80 based laptop. i'd
like to build a laptop based on what I suspect the designers at
Camputers would have built if they had access to the current zilog
offerings (and weren't smoking those special herbal ciggerettes :) )
so i'm wondering two things, 1. is there a modern equivilent to a 6845
crtc and if there is 2. could it drive an LCD display?
thanks in advance
Russell K. Davis
http://www.camputerslynx.info
Lee Hart
> decided to investigate building a Z80 based laptop...
> 1. is there a modern equivilent to a 6845 CRTC>
> 2. could it drive an LCD display?
The 6845 itself is pretty easy to get; any reason not to just use one?
It also isn't hard to get an LCD panel that accepts normal sync and
video just like a CRT monitor. The 6845 doesn't need to know the
difference. Or, you can use any of the parallel interfaced LCDs, and
write your own software driver. This is not bad at all; for example,
this is how the Radio Shack TRS-80 model 100/102/200/600 did their
display, and they "bit banged" it with a 2 MHz 80C85.
If I were doing this, I'd get a Heath H19 terminal logic board, which
has a Z80, 8250 UART, 6845 CRTC, RAM, ROM, ASCII keyboard, and
everything else needed. Put bigger RAMs in the bytewide ROM sockets. Use
it with an LCD display that emulates a CRT and you're most of the way
there.
--
Ring the bells that still can ring
Forget the perfect offering
There is a crack in everything
That's how the light gets in -- Leonard Cohen
--
Lee A. Hart, 814 8th Ave N, Sartell MN 56377, leeahart_at_earthlink.net
Russell Davis
>
> The 6845 itself is pretty easy to get; any reason not to just use one?
not really except i hadn't seen one for a while and although i did say
Z80 based i actually mean something like a Z80182 which might muck up
using a 6845
>
> If I were doing this, I'd get a Heath H19 terminal logic board, which
> has a Z80, 8250 UART, 6845 CRTC, RAM, ROM, ASCII keyboard, and
> everything else needed. Put bigger RAMs in the bytewide ROM sockets. Use
> it with an LCD display that emulates a CRT and you're most of the way
> there.
that's not a bad idea although i don't think it'll do for this project
as i want to build a camputers lynx alike but in a laptop form and the
lynx did some very wierd things with bankswitching and colour banks.
but definatly a great idea for a generic z80 based laptop
thanks
Russell
http://www.camputerslynx.info (currently fubar indexpage but
http://camputerslynx.info/technical.html works)
Russell Davis
>
> It will work if you pay attention to device access times. Watch the
> programming as there are a few "flavors" of 6845 and while socket
> compatable there are small programming differences.
>
ok thanks i'll remember to keep an eye on that
>>that's not a bad idea although i don't think it'll do for this project
>>as i want to build a camputers lynx alike but in a laptop form and the
>>lynx did some very wierd things with bankswitching and colour banks.
>
>
> Lynx?
>
at the risk of sounding like a complete and utter fanboy "the greatest
z80 based british 8bit home micro from the 1980s"
it was a wonderfully idiocincratic machine with a cult following
although poorly marketed and overpriced and very late to market.
some interesting points are that it was probably the last mass marketed
(if you can call about 50,000 ever made mass market) with a machine code
monitor in the roms.
the basic used floating point line numbers so that you could insert line
3.1415 between line 3 and line 4 if required :)
it had 4 colour banks red, blue, green and alt green which could be
turned off and on at will and used for extra program storage. it was
also possible to copy the rom to ram and then turn off the rom and run
it completly in ram.
it could run cp/m on the 128k (192k) versions and one of the usergroups
also got it working on the 96k version. another user group also made a
mod to it so it could also run sinclair spectrum software too
and a myrid of other things some braindead and some very nice.
unfortunatly my site about it went fubar so it's not quite workign right
but i'm in the process of fixing it but if you goto
http://www.camputerslynx.info/technical.html i have a set of technical
info there.
bst rgrds
Russell
http://www.camputerslynx.info/technical.html
Russell Davis
>>
>>that's not a bad idea although i don't think it'll do for this project
>>as i want to build a camputers lynx alike but in a laptop form and the
>>lynx did some very wierd things with bankswitching and colour banks.
>
>
actually rather than my previous post i should have just linked you to
http://www.camputerslynx.info/history.html although the portion about
the 96k cp/m being a myth is incorrect, it was reality
bst rgrds
Russell
Russell Davis
>
> The reason for the question is the name lynx is also a text based web
> reader for unix.
>
well we had it first :) along with LUG too :)
actually that's not the only problem when i talk to people (or search
the internet) about the lynx because there is also the atari lynx, a
couple of helicopters, some golf clubs etc. about the only thing i
haven't seen called lynx is a brand of kitchen sink and i wouldn't bet
against there actually being such an item.
> As to large versions of CP/M I've done 1mb CP/M 2.2 systems. Nothing
> special save for most (bulk) programs that run under CP/M have not a
> clue about extended (beyond 64k) memory. So to me a larger than 64k
> system goes without question as to it's existance and begs a question
> as to the use of the extra ram. Again most only use the extra ram as
> a ramdisk.
>
of course, i've seen and used those myself, they are nothing special.
however that is not why for a long time the 96k lynx running cp/m was
considered a myth. it was because
1. Camputers/Anston Tech. themselves had not been able to do it before
they went belly up. from what i hear from the people involved it was bad
enough with cp/m on the 128k lynx let alone the 96k.
2. because of the lynx's architecture especially the video banks and the
disk rom and their location within the memorymap it required a lot of
hacks, patching and an awful lot of ducttape. for a start on all lynx's
the code for reading and writing to video ram was copied from the rom to
the first 100 bytes of each videobank because when writing to a
videobank the rom was required to be switched out, this is not exactly
something that you'd want to do on a cp/m system :)
and there was also the problem that no two copies of any documentation
for the lynx ever gave exactly the same information for rom locations or
sysvars or even memorymap :)
but I definatly agree that in the normal course of things a > 64k cp/m
is nothing special however the camputers lynx is not a normal computer
in any shape or form :) if you ever get a chance to use one once you get
passed it's idiocincracies you'll either love it with a passion or
you'll hate it equally so.
bst rgrds
Russell