Bit banging serial port

[Robb Bates]

I bought a 1802 MemberCHIP card (the Smalls version) which uses the onboard I/O pins to do a bit banged serial port.  Fun little design!

Does anyone know if there's a bit-banged serial port for the Z80?

I believe the Orton does such a thing, but I think it uses the A15 address line as the output line.  That's a big sacrifice.  Using a simple 22V10 GAL or similar would be an easy I/O interface.  Unless someone else has another single chip solution (small DIP package, not a big wide one like a SIO2.

Robb

[Alan Cox]

If you need a single chip you might as well use a UART, but if you want to play then the Z80PIO or GPIO cards will do the trick. Bonus points for doing full duplex.

It's also possible to do serial using a Z80CTC if you want some fun. There were implementations that used a CTC for output pulse timing and wired the input side via NMI which combined with a free running timer gives you receive without a UART or polling.

Alan

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[Bill Shen]

Take a look at Muntz80, aka BB80, https://groups.google.com/g/retro-comp/c/QWPGzS1glTQ/m/PBZSsUrgAgAJ

The idea is using 22V10 both as a bootstrap ROM as well as bitbang serial, and also page out the ROM, so it can run CP/M.  The bitbang serial is half duplex, however.  I’ve combined both 6502 and Z80 designs into one pc board.  There is another similar design for 68008, but only prototype.

Bill

[Robb Bates]

That's impressive as heck!  Nice job.

[7alken]

hi all, using that interrupt pin as uart rx is cool )) ... but I quite recently (again) returned to the idea of custom post-boot debug channel even on MCUs (or just anywhere is some known GPIO only,, not having drivers for uart yet) to sense all of them for incoming clocks as $AAs from uart as bitbang (re)sync and even using that single line for uart rx/tx over rs-485 chips, here some recap of this weirdness:
https://chatgpt.com/share/68e62ec3-a3a8-8000-bda5-c96627a001ef
P.

[7alken]

and btw zeal8bit uses bitbanged serial port;
P.