System 80/Video Genie character generators. Compatible between versions?
Terry Stewart
there.
As you know I've been playing with these machines lately. Just for
fun I wouldn't mind doing a memory expansion on my refurbished System
80. I'm not that keen on the laborious 4116 chip method though. I'd
rather use 4164 ICs BUT I don't want to cut traces on my existing 16K
CPU.
There is a potential solution. I have another System 80 CPU board in
my parts bin. If I could get that working I could do the mod on that,
but keep the existing 16k one untouched. Then I could swap it back in
if I needed to.
One problem is the parts CPU board doesn't work at the moment and some
of the keyboard cable pins have snapped off at the base, but that's
all fixable. A bigger problem is that everytime I swap this parts
board in and out of the machine I'll have to deal with those damm
rigid plastic flat ribbon cables that connect the CPU board with the
video one. I'm so afraid I'm going to snap a pin, and they are a real
problem to connect up. Yet diagnosing a problem often requires
testing, removal, tinkering and more testing.
Now as well as a parts CPU board, I also have a parts/junk Video
board. All that is wrong with that (I think) is the character
generator. It's missing. If I wired up this parts/junk CPU board,
with the parts/junk video board in the bottom of my old spare system
80 case and used a PSU and a character generator from on of the other
machines I'd essentially have a forth system 80 computer, which I
could use to develop/test the memory expansion on the parts-CPU
board!. I wouldn't be too devestated if I broke the connecting ribbon
accidently with this setup as the arrangement is just for this
project. It's not like I would have wrecked one of the machines.
Now (if you have got this far) here is the rub. The parts/junk video
board is the early model board which was upper case only. All my
other system 80s are the revised board with lower case. I'm picking
the character generator IC then is different. How much different
though? Can I use one of the later character generator chips in this
early board? I wouldn't expect lower case of course, but would I get
characters at all?
I could try it and see but is there a possibility I might damage the
character generator IC by plugging it into one of these early video
boards??
Terry (Tez)
Terry Stewart
From checkin the circuit diagrams tonight it seems like they definitely are
not compatible. The early models use a 2513 IC for the character generator
and later ones a 52116. On the former the 5v line comes in at pin 11 and on
the latter at pin 25!
I don't think a try out would be healthy!
Terry
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06:36:00
Peter Nield
the 52116 which fit into the 2513 socket to fix that - with a wire to the
extra static RAM chip piggy-backed onto one of the other video RAM chips and
the D6 (?) line.
--------------------------------------------------
From: "Terry Stewart" <te...@webweavers.co.nz>
Sent: Tuesday, July 13, 2010 8:07 PM
To: <eaca-di...@googlegroups.com>
Subject: Re: System 80/Video Genie character generators. Compatible between
terry stewart
Yes, you are right. This spare/junk board I'm talking about actually came
off my original System 80. It had a lower case mod. The reason the
character generator is not there is that it developed a fault, so I replaced
the whole video board with one of the later model ones (with l/c) and threw
the l/c modded character generator out years ago. I clearly remember a
piggybacked board with what I think was an EPROM on top of it. And there
was a wire to another chip.
And now as I look at the board I can also see the extra static RAM piggy
backed onto of the other video RAM chips, just as you say.
I should have kept the piggy-back board but you never imagine you'll ever
want these things again when you toss them, do you.
Terry
Thinking back 28 years, this
Knut Roll-lund
From: Terry Stewart [te...@webweavers.co.nz]
>
> I'm seeking some advice from System 80s/Video Genie hardware gurus out
> there.
>
> As you know I've been playing with these machines lately. Just for
> fun I wouldn't mind doing a memory expansion on my refurbished System
> 80. I'm not that keen on the laborious 4116 chip method though. I'd
> rather use 4164 ICs BUT I don't want to cut traces on my existing 16K
> CPU.
4164 don't use 12V and -5V, only 5V so if you want to put them in the 4116s sockets you need to cut traces.
If you instead make a daughter-board and connect it to the sockets etc. this can be done without damaging the card.
Alternately you can do something like a project I'm working on: Using an SRAM - the one I have here and plan to use is Samsung K6X1008C20-BF55. I will put it on a card that plugs into the Z80 socket and the card will have a socket for the Z80 as well as decoding logic for the SRAM (similar to a DD kit). I plan to make the design transparent so that bankswitching can be used to switch in the original RAM. I will probably use some GALs to do the logic etc. The card I plan to use (I have several) is an old card made where I work it is actually meant for i8088 adding an i8087. It does have 40pin sockets so I will just have to modify this card a little so it fits Z80. The logic and the SRAM is so so I'll just stick those to the borad next to the 40 pin socket.
I will intercept MREQ and IORQ signals so that access to the SRAM and bankswitch registers can't create conflicts. I will have to do something about letting the MREQ signal through for refresh though. Someone suggested to make it compatible with one memoryexpansion that I don't have. This is possible but I would probably have to add extra logic for that. The original plan was to make it compatible with the RAM kit I have in my old genie (General Northern - port 127). I was also thinking I might put in a "sliky" type interface too (Apple][) useful for ramdisk. But, on the other hand, maybe it is best to keep it simple.
This project has not had any progress lately but it is on my desk next to me. Something clear for the other RAM kit would help, a list of i/o ports and what they do would help.
On conflict -> those I/O ports the SRAM supports will of course be unavailable for other hardware.
I think default should be 48K SRAM, leaving original RAM and EI RAM unused but refreshed.
> There is a potential solution. I have another System 80 CPU board in
> my parts bin. If I could get that working I could do the mod on that,
> but keep the existing 16k one untouched. Then I could swap it back in
> if I needed to.
>
> One problem is the parts CPU board doesn't work at the moment and some
> of the keyboard cable pins have snapped off at the base, but that's
> all fixable. A bigger problem is that everytime I swap this parts
> board in and out of the machine I'll have to deal with those damm
> rigid plastic flat ribbon cables that connect the CPU board with the
> video one. I'm so afraid I'm going to snap a pin, and they are a real
> problem to connect up. Yet diagnosing a problem often requires
> testing, removal, tinkering and more testing.
>
> Now as well as a parts CPU board, I also have a parts/junk Video
> board. All that is wrong with that (I think) is the character
> generator. It's missing. If I wired up this parts/junk CPU board,
> with the parts/junk video board in the bottom of my old spare system
> 80 case and used a PSU and a character generator from on of the other
> machines I'd essentially have a forth system 80 computer, which I
> could use to develop/test the memory expansion on the parts-CPU
> board!. I wouldn't be too devestated if I broke the connecting ribbon
> accidently with this setup as the arrangement is just for this
> project. It's not like I would have wrecked one of the machines.
Those cables are bad. In my old genie I have replaced them all. I made cables with "berg" type pins so they could be disconnected but it has not become a final solution because sometimes I get bad contact and the plugs need to be wriggled to make it work. In my "new" genies I am very careful with those cables because they work well as it is.
>
> Now (if you have got this far) here is the rub. The parts/junk video
> board is the early model board which was upper case only. All my
> other system 80s are the revised board with lower case. I'm picking
> the character generator IC then is different. How much different
> though? Can I use one of the later character generator chips in this
> early board? I wouldn't expect lower case of course, but would I get
> characters at all?
>
> I could try it and see but is there a possibility I might damage the
> character generator IC by plugging it into one of these early video
> boards??
>
I see you already figured that out. 2732 can be used but you need to swap some pins, can be done with a socket for wire-wrap. I have such a setup for the first ROM which I have replaced with a 27??. I have replaced the chargen with a 2732 (IIRC) where I let it generate the full character set (also block graphics). If you like I can make you such a 2732 as I have both spare EPROMs and a programmer that can do them. Note that (in my experience) many, more recent programmers claim to do 2732, 2732A and 2716 but really can't.
BTW a comprehensive list of I/O ports as they were used in different products for System80/Genie/TRS-80 would be something great to have. Could we create such a list and put on our sites.
BTW2 I think I discovered that the Genie EI (unmodified) is not well designed so putting any device in parallel to it that reads an I/O port is not good. So I modified mine so it only drives the transiever when the I/O prots of the EI is read. I should document this...
Knut
terry stewart
I appreciate that comprehensive post. Don't worry about burning me an EPROM
for now. Given the "issues" I've decided to leave playing around with
memory expansion on the spare board for the time being.
In the mean time I'm testing the market with the System 80 I've just
refurbished. See
http://www.trademe.co.nz/Computers/Vintage/auction-303443967.htm
I don't want to let it go, but I strongly desire to add a Model III/IV to my
collection and the only way to do that seems to be to ship them to NZ at
eye-popping shipping costs. I've got to raise some money by selling off a
bit of gear. It might not sell, as I've put quite a high starting price on
it for a vintage computer which is not in original condition. That's what
it's worth to me to keep though, so if no one bids it will just be used as a
hobby machine (then I probably WILL have a crack at the memory expansion).
I removed the RCA cord and that single holder. The machine's not original
condition anyway and it just made it look untidy. Most modern TVs have an
RCA composite video input nowadays anyway.
I agree about documenting. These technical things should go on a website
somewhere so they are accessible.
Terry
----- Original Message -----
From: "Knut Roll-lund" <kr-...@online.no>
To: "Eaca discussion" <eaca-di...@googlegroups.com>
Sent: Tuesday, July 13, 2010 11:20 PM
Subject: Re: System 80/Video Genie character generators. Compatible between
versions?
Hi
Knut
--