15 Aug
2005
15 Aug
'05
6:05 p.m.
An early example of a bit banger serial interface was the Motorola 6800
MIKBUG Monitor ROM. It used a parallel interface chip (MC6820 PIA) as a
bidirectional serial interface. It would work at 110 and 300 baud (some
people clocked it at 1200 baud.) This was the used in original (1975)
Southwest Technical Products 6800 computer. Motorola had a real UART (MC6850
ACIA) at the time so I don't know why Motorola did this. SWTPC later
switched the their own Monitor ROM and a MC6850 serial port.
http://www.swtpc.com/mholley/swtpc_6800.htm
Michael Holley
15 Aug
15 Aug
6:44 p.m.
New subject: Bit Banger was Analog modem emulator?
In message <001e01c5a1fe$ad9c6480$0300a8c0 at downstairs2>, "Michael
Holley" write
s:
An early example of a bit banger serial interface was
the Motorola 6800
MIKBUG Monitor ROM. It used a parallel interface chip (MC6820 PIA) as a
bidirectional serial interface. It would work at 110 and 300 baud (some
people clocked it at 1200 baud.)
That reminds me or another little machine from Motorola. They
called it the Educator II (and was the first computer I ever
owned). Their cassette interface worked pretty much the same
way. They toggled a pin on the PIA in software for a simple
FM encoding at 110 baud. Even the receive side was software.
Brian L. Stuart
16 Aug
16 Aug
3:51 p.m.
New subject: Bit Banger was Analog modem emulator?
That reminds me or another little machine from Motorola. They
called it the Educator II (and was the first computer I ever
owned). Their cassette interface worked pretty much the same
way. They toggled a pin on the PIA in software for a simple
FM encoding at 110 baud. Even the receive side was software.
Many microcomputer cassette interfaces are bit-banged. It works quite
well for that application, because you know when data could be coming
from the cassette (the user has executed a LOAD command
or whatever it's
called), so you can put the microprocesosr into a loop looking
for
transitions on the input pin.
It works less well for linking to a terminal, because you have know idea
when the user is going to press a key :-)
-tony
3:48 p.m.
An early example of a bit banger serial interface was the Motorola 6800
MIKBUG Monitor ROM. It used a parallel interface chip (MC6820 PIA) as a
The earliest desktop comuter I know of with a bit-banged serial port is
the HP9830.
There were 2 serial interfaces for that machine, I'll probably get the
model numbers wrong, but here goes.
The 11205 was a hardware serial interface, using TTL shift registers,
etc. You set the baud rate in hardware (links or switches on the PCB),
the 'computer side' of the interface looked much the same as the other
interfaces for the 98x0 series, it was commonly used to link up serial
peripherals, printers, etc.
The 11206 was a bit-banger. It worked with a terminal emulator ROM which
turned the 9830 + 9866 into a printing terminal with local storage (in
the BASIC program area of the 9830's memory, which could then be saved on
cassette and loaded back again). The baudf rate was set by a keyboard
command, anything from 3 to 440 baud IIRC (strange limits, those...)
I have never seen a bit-banged RS232 (or current loop) port on a
minicomputer. Anyone know of one?
-tony
17 Aug
17 Aug
1:20 a.m.
Tony Duell wrote:
I have never seen a bit-banged RS232 (or current loop)
port on a
minicomputer. Anyone know of one?
The HP 2116, 2115, 2114 minis (1966-70) used bit-banged serial.
In addition to bit-banging for a single device, there was an I/O interface
for handling up to 16 terminals via bit-banging, the interface being - in
essence - merely a 16-bit parallel port with each terminal assigned to one of
the 16 I/O bits. This was used by the 2000A timeshared BASIC system.
(Between bit-banged I/O for multiple terminals, interpreting the BASIC programs
and timesharing overhead, it's amazing the processor found any time to do
anything 'useful'.)
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ard＠p850ug1.demon.co.uk -
blstuart＠bellsouth.net -
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swtpc6800＠comcast.net