character codes, was RE: Really stupid PDP assembler question

From: Tony Duell <ard_at_p850ug1.demon.co.uk>
Date: Sun Jun 27 12:26:53 2004

>
> Tony,
>
> I was actually refereing to even earlier printing calculators that had a
> single vertical bar per position with the numbers 0-9 on each one. The bar

I remember those, just, but only on fully mechanical calculators. But I
also haev a Victor Comptometer calculator with solenoids mounted over the
keys that was used as a printer on a data logging system, so maybe such
machines were hacked onto computers too.

> would be raised/lowered an an individual striker per position would fire.
> There as no left-right movement along a "carriage". The first machine I saw

I've seen early 70's calculators with tiny drum printers. A drum the full
width of the paper -- perhaps 15 columns -- with the digits, -ve sign,
decimal point, round it and a row of hammers that print the approriate
characters. I've also seen them with a typewheel per column which were
positioned and then all columns printed simultaneously. And then I've
seen one with a carriage containing a single typewheel and a hammer
mechanism.

One of the strangest printers I've seen came off the data logger for a
gas chromatagraph (a Kent Chromalog II if anyone wants to try to find
details). There was a typewheel per column with a solenoid to step it
round one posisition, and a switch that gave a carry function. It was
essentially a long ripple counter. There was a hammer assembly the full
width of the paper. You fed in the pulses (the instrument was
essentially an integrator), and at hte approrpriate time you fired the
hammer.

I can't rememebr how the reset-to-zero worked. I don't think there was a
separate solenooid for that. Maybe you just fed in a clock signal to all
solenoids together and turned each one off when the carry contact flipped
or something.

-tony
Received on Sun Jun 27 2004 - 12:26:53 BST