Bit Banger(s) we all have known.
ard at p850ug1.demon.co.uk
Sun Aug 21 12:57:51 CDT 2005
> Well (since you asked) the original serial interface for the HP 2116
> computer (around 1966 or so) was a serial bit-banging interface. You
> needed to assemble the byte from the ASR-33 (or 35, take your pick)
> teletype a bit at a time. They later had the bit assembly/disassembly
> register (this WAS pre UART chips) that did al the work. Unfortunately
> the "parallel" serial interface was only half duplex, as it used the
> same register for both assembly and disassembly. The "serial" (bit-
> banging) serial interface IIRC did not have this restriction.
COme to think of it, that's very similar to the serial interfaces for the
The hardware one only had a single shift register for both Tx and Rx. I
think there was a status line brought out (at RS232 levels) on one of the
handshake pins that indicated to the peripheral when the calcultor was
expecting input. It's a half-duplex device.
The bit-banger had no common circuitry between the input and output, and
could be used in full-duplex mode. It was only supported on the 9830
(BASIC-language) machine, but I can't see a hardware reason why there
couldn't have been firmware written for it on the other machines in the
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