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From: don on 18 Oct 2009 15:16
don wrote:
> I may have missed it, but how about the code in the existing ROMs.
>
> Do you have any idea on how to add code so it will work with the
> existing code base ??
>
> Do you have schematics of the original unit ??
>
> As others have mentioned, the hardware should be easy to connect with
> some care.
>
> The software is going to be the biggest hurdle.
>
> don

Reading your web site, I noticed that you did not stated what you were
going to do with the serial port once it is installed.

I would suggest replacing the ROM chips with RAM chip(s), this would
allow you to run a Bootloader.

Google found lots of Bootloaders:
http://www.google.com/search?q=Z80+bootloader

A smaller UART chip would be the SCC2691, Digikey has them for $5.40 for
one.

Good Luck

don
From: Nico Coesel on 18 Oct 2009 16:00
"Commander Dave" <cmdr-dave(a)spamcop.net> wrote:

>
>"Nico Coesel" <nico(a)puntnl.niks> wrote:
>> "Commander Dave" <cmdr-dave(a)spamcop.net> wrote:
>>>
>>>First, was there a better UART that I could have chosen?
>>
>> The 16C550 is an excellent choice. It has FIFOs so the software
>> doesn't have to service it all the time.
>
>That's good to hear. My question is really just curiosity at this point as I
>am somewhat locked into the design I have for now. If there was a better
>choice I would have probably put it into a future design.
>>
>>>Second, I have to tap all the signals from the bottom of a card cage by
>>>running individual wires to my board. I currently have this hard wired
>>>which
>>>is a pain for debugging purposes. I need a connector system that takes
>>>these
>>
>> What you need is an small program that tries to read & write from the
>> UART. IIRC register 7 of the UART is a scratch pad register (unused
>> but can be written & read). Try and see if you can read and write data
>> to that register. This will verify whether the UART can be accessed by
>> the Z80 or not.
>
>I actually did what you have suggested. I have a program that initilized the
>UART and then read back the registers. Unfortunatly, every register just
>returned the decimal number 12, even when the UART wasn't in the socket.
>This indicated to me that the Z80 isn't talking to the UART correctly. I
>suspect that it is my wiring on my prototype. Since the 16C550 is
>discontinued in the DIP 40 format, I went with a PLCC format which was
>difficult to wire up. I have a PLCC to DIP converter board ordered which may
>help with this problem. I also thought about breadboarding the port
>addressing circuit with some latches and LED's to see if my design is even
>working at the port decoding level. Still considering that option, but
>that's more I would have to figure out how to do. I'm learning as I go...

Wiring a PLCC socket is not more difficult than a DIP socket. You'll
need to figure out which pin goes where first though. I suggest you
get a simple oscilloscope (a 20MHz will do) to do some measurements
(like the port decoding).

--
Failure does not prove something is impossible, failure simply
indicates you are not using the right tools...
"If it doesn't fit, use a bigger hammer!"
--------------------------------------------------------------
From: Commander Dave on 18 Oct 2009 17:15
"Nico Coesel" <nico(a)puntnl.niks> wrote in message
news:4adb732b.902338000(a)news.planet.nl...

> Wiring a PLCC socket is not more difficult than a DIP socket.

Oh, I don't know about that... it was definitely harder for me, but again,
I'm a newbie at building boards. Another reason I wanted the DIP 40 format
was so I could breadboard it initially... those PLCC sockets don't fit on a
breadboard AFAIK. Since I have an adapter on the way (found one for $6.95
shipped), it's pretty much a moot point now.

>You'll need to figure out which pin goes where first though. I suggest you
> get a simple oscilloscope (a 20MHz will do) to do some measurements
> (like the port decoding).

I would like to get an oscilloscope, but I am really cash poor. I
practically have to scrounge money for the small parts that I buy. One of
these days I'll snatch one up cheap, but until I get the money I have to
work with what I have.

Thanks for the suggestions,
-Commander Dave


From: Commander Dave on 18 Oct 2009 17:38
<don> wrote:
> Reading your web site, I noticed that you did not stated what you were
> going to do with the serial port once it is installed.
>
> I would suggest replacing the ROM chips with RAM chip(s), this would allow
> you to run a Bootloader.

My intentions are to have a small monitor program in EPROM with the ability
to download program code into RAM and then have the machine execute it. It's
mainly for testing and debugging purposes. Once I have the code solid, I
would burn the program into an EPROM and put it in the game permantly.

I do use a Gorf arcade emulator (MAME) to do the gross debugging, but
sometimes things that run on the emulator will not work on the real hardware
or it will have different results. Burning EPROM's to test code in the real
machine is a pain, but compiling and downloading to the machine would be
quick and easy.

As for replacing the ROM with RAM and running a bootloader, it seems like
the modfications would be just as much work as building a serial port, but
honestly, I would have to research the information you gave me on
bootloaders to make an informed decision. My main concern is that I don't
want to hack around on the original hardware if I can avoid it. By
connecting a serial port, I only have to run wires from the bottom of the
cardcage to a external board and just have to burn one EPROM that would go
in an extra socket on the original board. I modified the original game code
so that if I flip the diagnostic switch on, it looks for this extra EPROM,
and if it is there, jumps to my code. If it isn't there, it runs the game as
normal.

Sorry I got so chatty.... I really need to copy and paste this into my
project web site. I will look into what you are suggesting, however. :-)

> A smaller UART chip would be the SCC2691, Digikey has them for $5.40 for
> one.

Interesting! I glanced over the datasheet and it looks like a viable
alternative with a smaller footprint in the DIP format. I'm kinda locked
into the 16C550 for this run, but I may use the chip you suggest in any
future projects (or perhaps future incarnations of this one). Thanks!

> Good Luck
> don


From: a7yvm109gf5d1 on 18 Oct 2009 18:06
On Oct 18, 4:15 pm, "Commander Dave" <cmdr-d...(a)spamcop.net> wrote:

> I would like to get an oscilloscope, but I am really cash poor. I
> practically have to scrounge money for the small parts that I buy. One of
> these days I'll snatch one up cheap, but until I get the money I have to
> work with what I have.
>
> Thanks for the suggestions,
> -Commander Dave

Where are you located? You sound like someone that can benefit from
people trying to cleanup their place.
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