as the title suggests, can anyone point me to code examples for bit-banged serial, please? I'd like to use a 6522 but the hardware doesn't matter that much.

tia. cheerful regards, Mike, K8LH

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If you could find a listing of the TIM monitor ROM I’m pretty sure that it uses bit-banged serial on the 6532. The monitor listing is in the TIM manual and should be easy to find.

I posted some SPI routines for 6522 here. There're also some suggestions regarding which port bits to use for what. The priority is speed, and the routines require less than 20 clocks per SPI bit.

-- Jeff

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In 1988 my 65C02 got six new registers and 44 new full-speed instructions!
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A previous thread cooks up a serial driver, and also links to MartinB's implementation (UPURS) as seen on stardot:

1Mhz 6502 bitbang 57kbaud

Edit: and a couple of our mos6502 weekly posts too, indexed here:

Bit-banged communications on Commodore (or use a UART)
Bit-banged serial connections (on Beeb), supporting remote storage and a remote filesystem

Bitbang serial receive is more difficult than bitbang serial transmit. CRC65 has a hybrid solution where the serial receiver is in hardware (implemented in CPLD logic) but bitbang the transmitter to save CPLD resources. The code for bitbang transmitter is here, viewtopic.php?f=6&t=6440&hilit=Bitbang+serial&start=15#p81149
Bill

pagetable.com has some of the imho best commented C64 Kernal listings where you can find both:

Synchronous bit-banged serial: The serial IEC send (CIOUT) and receive (ACPTR) routines:
CIOUT: https://www.pagetable.com/c64ref/c64disasm/#EDDD
ACPTR: https://www.pagetable.com/c64ref/c64disasm/#EE13

Asynchronous bit-banged serial: The RS232 code, hidden within the BASIN and BASOUT routines:
Output to RS232: https://www.pagetable.com/c64ref/c64disasm/#F208
Input from RS232: https://www.pagetable.com/c64ref/c64disasm/#F1B8
I find the RS232 code harder to understand (in fact, I really don't understand it) as it uses CIA-2 timer based NMIs.

I did the software for Lee Hart's "6502 Badge". That used the IRQ pin as the serial receive. Output was created by storing an 8 bit write to the EPROM area in a latch. Bit 7 of that latch was the serial TX.

The software used cycle counting to generate a 9600 baud half duplex signal. It included a 128 byte receive buffer to help with xmodem file transfers.

More info can be found here -> http://sunrise-ev.com/6502.htm

Daryl

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