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Very simple IO board
Posted: Fri May 09, 2008 12:41 pm
by sirmorris
Hi all,
Would it be of interest if I were to write a simple 'how-to' for those of you who are happy to solder a few wires? It would require just 2 or 3 chips, a prototype board and a zeddy edge connector.
The IO board would have 8 lines in each direction and this would be the 1st step to adding flash memory in the form of MMC cards to the zeddy...
If there was sufficient interest I might consider putting together a kit of parts for cost price + postage. You would need to be able to solder though - there's no way around this
Charlie
Re: Very simple IO board
Posted: Fri May 09, 2008 8:56 pm
by RWAP
I can also probably help in that if any hardware projects get off the ground and there is enough interest, I have found a good electronics engineer, who can help design, prototype and build finished products which I can then offer for sale via my website.
Re: Very simple IO board
Posted: Fri May 09, 2008 9:09 pm
by Andy Rea
as i posted earlier today i designed and built a simple IO for ZX81 using just 3 IC's A 74ls32 , A 74ls273, and a 74ls245.
http://homepage.ntlworld.com/deborah.cl ... zxio-b.jpg
that image shows the output(top ic 74ls273), connected to the inputs (bottom ic 74ls245) making it a psuedo 8 bit bi-directional bus (either end can drive a line low, but not force it high) but if you didn't connect the inputs to the outputs in such a way and remove the diodes you'd have 8 outputs and 8 inputs with which your free to do whatever you liked.
A6 on the zx81 edge connector needs to by low i used port $BF as this didn't collide with anything else i was already using.
Andy
Re: Very simple IO board
Posted: Fri May 09, 2008 10:57 pm
by sirmorris
Well seeing as you showed me yours...
This is addressed at port 7 for in, and port 17 for out.
4 chips, though..!
Re: Very simple IO board
Posted: Sat May 10, 2008 12:23 am
by Andy Rea
more chips equals more functionallity, it's a more elegant decoding scheme for sure. Nice one Sir Morris.
Regards Andy
Re: Very simple IO board
Posted: Sat May 10, 2008 3:03 pm
by sirmorris
Ahem I must admit I didn't invent the decode scheme - It came from a board by one of the zx-team via Siggi!
The input isn't latched either, there was a reason I'm sure but the mists of time have passed over me since I did it
Re: Very simple IO board
Posted: Sat May 10, 2008 8:44 pm
by XavSnap
Re: Very simple IO board
Posted: Sun May 11, 2008 10:42 am
by sirmorris
Xav - is your board is memory-mapped in the 8-16k area? And is it output only?
It looks like you make your own PCBs too - I haven't tried this yet though I think I might have a go. It's the investment in chemicals and the rest of the kit that puts me off..
Re: Very simple IO board
Posted: Mon May 12, 2008 3:14 pm
by XavSnap
HI,
Xav - is your board is memory-mapped in the 8-16k area? And is it output only?
It can be mapped on the ROM or in unused memory segments! (Poke 7777,0 is an exemple)
Output only if used on the ROM, but in top memory input can can be available ? (Rom mirroring?)
It looks like you make your own PCBs too - I haven't tried this yet though I think I might have a go. It's the investment in chemicals and the rest of the kit that puts me off..
True!
