Less simple IO board

[sirmorris]

A colleague was putting a plate of PCBs in for fabrication and I managed to blag a few square inches. I had to whip this up double-pronto and I've made loads of mistakes

This is my first ever fabbed board and hopefully it won't be the last. Next time I won't put the silkscreen over a via...
And I'll try to remember to put a regulator on...

[yerzmyey]

What does it do?
Just curious.
I know nothing about soldering and circuits.

[sirmorris]

It's an I/O board.

The big IO chip is an 8255, quite a common part. It has 24 IO lines with selectable directions. It's usually found in parallel ports and similar applications.

The 2 smaller ICs are for address decoding - they watch for a particular set of conditions on the zeddie's IO and address lines and enable the IO chip as required.

C

[tdg8934]

Sir Morris,

Did anything happen with you I/O board (8255 or other)? I was originally thinking of doing this before I got the ZXpand-AY with I/O support. I have worked with the 8255 years ago and would like to know if that is the way to go or is there anything more modern to use.

Thanks,

Tim

[sirmorris]

There was a mistake on the board which is fixable but it stopped me in my tracks. I never even got to testing it.. I don't know if I have the schematic still but I'll have a look.

If you need 24 lines of IO then you need 8255!

[PokeMon]

If you need I/O not very fast you could use a combination of shift registers and a bit bang interface with just input and clock (2 signals).
This is very cheap - you need only a piece of software to put all outputs correctly.
74LS164 or better 74HCT164 are very cheap, can hold 8 bits per IC and simply extended to an infinite loop
Just connect the last bit with data input of next 164 chip.

For LED applications it would be fast enough and you can simply have 80 I/Os with just 10 ICs - cost about 0.50 USD per piece or about 5 USD for 80 I/Os I think.

[tdg8934]

Here is some 8255 24 LED output work I did with a Parallax BASIC STAMP 2 in 2006 and later converted it to a Parallax SX-28 for SXB (BASIC like language). I also accomplished similar work with some 74HC595(s). Open the *.BS2 and *.SXB files with a text editor like WORD PAD.