Serial Port Design for Z80 - Questions
in [Design]
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From: Frank Buss on 18 Oct 2009 14:09 Commander Dave wrote: > First, was there a better UART that I could have chosen? The 16C550 seems to > have been around for quite awhile. I am looking for mainly availability and > simplicity rather than cost or other factors. The "authentic" solution would be to use a Z80 SIO :-) http://vt100.net/manx/details/40,10863 I think I have one in my basement, if I can find it, but there are even some available at eBay. -- Frank Buss, fb(a)frank-buss.de http://www.frank-buss.de, http://www.it4-systems.de
From: Commander Dave on 18 Oct 2009 14:10 "Les Cargill" <lcargill99(a)comcast.net> wrote: > > I don't know where to start. Nice looking schem, though. I don't mean to > sound rude, but this is a bit like saying "I would like to make a > pig fly, and here's the design for the wings." There is a step or > two missing :) You didn't come across as rude at all. Actually the concept is quite easy. Don't let the fact that the object is an arcade machine throw you, think of it as only a Z80 computer and I'm just adding a serial port to it. I agree that from your perspective that there is many steps missing, such as I didn't explain about the programming or how I worked out the port addresses and such, but for this post's purpose I just need a few specific pieces of information related to the electronics. I've already thought a lot about how to make the pig fly and build the wings, I'm just wanted a few suggestions on how improving the wing design slightly. :-) I suppose my last question which was "if you see any errors in the design" was mainly what you were referring to. It was only meant for people to point out errors in the schematic at hand, not errors in the overall design. For example, an experienced person may look at the design and say "Oh, he has the IO REQUEST line backwards" or "He has the port decoding wrong for the addresses he has specified". Just simple, little things. > I really feel the better part of valor here is to find a ROMulator > ( a little box that acts like a ROM, but already has a > serial port, if not also Ethernet ) > > http://www.hondata.com/romulator.html I've considered that option, but for reasons that would be hard to explain, I decided against it. One reason is that the Gorf machine has many ROM slots (it's old technology) and also I'm looking for something that I can leave attached to the game permantly (so to speak). I also wanted to try my hand at actually designing and building something rather than a store bought solution. It's not all about the end result, you see... it's kind of a hobby thing too. > or even a Z80 in-circuit emulator. <<<snip>>> > Here's an "open source" ICE: > http://www.tauntek.com/Z80-In-Circuit-Emulator.htm They're going the way > of the dodo bird, so hurry! I actually looked at this before hand when it was available as a kit, but again decided againt due to the reasons I mentioned above. Again, the main reason is that I want to design and build, not buy. But both the ROM emulator and the Z80 ICE were excellent suggestions, which I appreciate. > > Good luck. Thanks Les... I appreciate your reply and all your suggestions. > Les Cargill
From: Commander Dave on 18 Oct 2009 14:55 "Frank Buss" <fb(a)frank-buss.de> wrote: > Commander Dave wrote: > >> First, was there a better UART that I could have chosen? > The "authentic" solution would be to use a Z80 SIO :-) > http://vt100.net/manx/details/40,10863 I intially rejected the Z80 SIO because it looked to me to be a bit more complicated to wire up than the 16C550, but it might just be my inexperience. Thanks for the suggestion, I will keep it in mind.
From: don on 18 Oct 2009 15:00 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
From: Commander Dave on 18 Oct 2009 15:09
"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... Thank you for the helpful suggestions! |