[GreenKeys] Model 40, Anyone?

[David I. Emery]

On Fri, Jun 12, 2020 at 09:10:36PM -0700, kn7sfz wrote:
> And what might happen if you dropped the link to 300 or even 110bps??? Is 
> there some kind of buffer that would wait and print an entire line when 
> ready or would the CPS just drop?

	They had a big VLSI NMOS chip that did all that... and indeed
it was a line printer, printing a line at a time from a buffer.   The
chip figured out what letter on the chain was going by which hammers
at any instant and fired them at an appropriate time to print the
desired character.   This could take place at several points on a
line at once (there were 80 or 132 hammers)...

	IIRC (it has been a LONG time) the chip drove a small trip
solenoid per character position on the line that caused the hammer arm
for that character position to engage a rotating bail... banging it onto
the moving type pallet on the chain.   So unlike some other line printers
of that era the actual force that printed the character was mostly from
the motor that drove the bail rather than from a much higher power electronic
print hammer driver... that was common in other line printer designs
of the era.

	My memory is that the chip waited until a received line was complete
before printing any of it, but that might not have been always true in
all cases, I am not sure about that detail this long removed from it.
It wasn't readily possible to see the line being printed, so the value
of incremental printing was pretty limited.

	And going at full speed it wasn't readily possible to read the
text as it was being printed... either.

	The ones I used on an Intel microprocessor SW development system
in 1981/82/83 had RTS/CTS (and XON/XOFF) pacing provisions so the flow of
characters to the printer could be controlled by the printer and it was
possible to set the RS-232 baud rate to feed the printer as fast as it
would go without worrying about padding characters for timing as you
need to with most mechanical printing devices.

	I also vaguely remember there was a provision in the logic to
print only a certain number of characters at once... so as to avoid
excessive mechanical load on the motor and chain... thus avoiding the
pathological case of printing all 80 or 132 character positions at once with
a suitable message...

-- 
  Dave Emery N1PRE/AE, die at dieconsulting.com  DIE Consulting, Weston, Mass 02493
"An empty zombie mind with a forlorn barely readable weatherbeaten
'For Rent' sign still vainly flapping outside on the weed encrusted pole - in 
celebration of what could have been, but wasn't and is not to be now either."