30 Jun
2010
30 Jun
'10
1:23 p.m.
The origian
laser controller was on/off only (but not a simple design due
to the speed reuired).
Thankfully fast opamps aren't as rare as they used to be. Fast MOSFETS
moreso :) There was a DAC (IIRC discrete resistors in the
SX engine) to steh laser diode current,
It was current-regulated? That's an odd choice if you're going to switch a diode on and off at ~20MHz. Would have thought the
current regulation
loop would have had kittens every time the current was turned off, and
put a current spike through the diode at every off-to-on transition
(unless it was (*really* carefully designed).
It was cerefully designed (I did say it was complicated). IIRC it
switched the current source between the laser diode and a dummy load
accordinmg to the state of the drive input. It had to work at nearly 30MHz.
And BTW, overshoot on the drive currend will do nasty things to the laser
diode!
> Would uofficial scheamtics of the SX engine be
any use?
That's _unofficial_ of course...
If they include schematics of the laser driver and scanner motor driver?
Hell yeah.
Includes every part of the printer. Even the PSU and EHT block. I will
see what I can do.
Not AFAIK (or
at least the CX enginer controllers I've worked on don't).
The motor speed is controlled by a PLL-tpye thing (the chip on the motor
PCB in the scanner unit, with an 'FG' coil on the PCB). Any slight errors
in the bir rate would slightly cheange the size of the printout, but who
actually checks that (rememebr a crystal almost certainly better than 1
part in 1000, so the erors will not be large).
Right, so it's locking the motor off of the incoming bit stream? When you explain it like that, it makes far more sense than
locking the
driver off of the motor.
Sounds right.
I think the PERQ scheamtics books are on
bitsavers. Take a look at the
OIO board schematics, you should find a CX-VDO printer interface there.
Agian I shouldbe able to provide details of the state machine ROMs, etc.
I think I've found it... PERQ T2 schematics, volume 2. The PERQ 1A schematic set doesn't seem to include the OIO
board, but there's a Canon
LBP-only OIO board for the T2.
The OIO boards fit all classic PERQs (it's the only board that is totally
universal like that). AFAIK the 3 OIO versions (ethernet, cannon,
etherent and canon) were all built on the same PCB, with just different
ICs missing.
I had a quick look at the PCB photos too... I've never seen anything
quite like them. What are they, wire-on-epoxy? They look like someone
Some of the prototypes/early ones were. But AFAIK all later PERQ boards
were notmal PCBs. Certainly every OIO I've seen has been a normal PCB.
-tony