30 Oct
2017
30 Oct
'17
1:13 p.m.
From: Paul Koning
Sent: Friday, October 27, 2017 12:07 PM
True if you have a TTL machine. 6600 is discrete
transistor, and the actual
transistor specs are nowhere to be found as far as I have been able to tell.
But that doesn't directly relate to gate level
emulation. If you have gate
level documentation you can of course build a copy of the machine out of
actual gate-type parts, like 7400 chips. Or you can write a gate level model
in VHDL, which is not the most popular form but certainly perfectly
straightforward. Either way, though, you have to start with a document that
shows what the gates are in the original and how they connect. And to get it
to work, you need to deal with timing issues and logic abuse, if present. In
the 6600, both are very present and very critical. For example, I've been
debugging a section (the central processor branch logic) where the behavior
changes quite substantially depending on whether you favor S or R in an R/S
flop, i.e., if both are asserted at the same time, who wins? And the circuit
and wire delays matter, down to the few-nanosecond level.
Paul,
I asked the Principal Engineer here, who has spent the last 3 years making our
6500 run, about transistors in the 6000 series. He replied:
Near as I can tell, the 6500 uses 2n2369 transistors in a slightly shorter
version of the to-18 package. I have had good success with both the 2n2369
for replacements, and mmbt2369 for the modules I have re-manufactured.
Since the flip-flops are merely cross coupled transistors, if they are both
set at once, both outputs will be true. In my experience, the set and reset
run on different phases of the clock, so that doesn't happen.
What you see on the logic diagrams can be interpreted this way: Each arrow
is a transistor, with the emitter tied to ground. The base usually has
about a 150 ohm resistor. The circle or square is the collector pull-up
resistor, so in the example of the PC module in 1n15 of the 6500, there are
two gates that can set flip-flop 0, and they come in on transistor 15, and
17, and the other side of the flip-flop comes in on transistor 19. All
three transistor collectors are connected together to 1 pull-up. If the
output pin does not go anywhere internal to the card, there will be a 120
ohm resistor in series with a diode to ground on it. If it does go
somewhere internal to the card, they will leave off the resistor/diode, as
the load will provide it.
Hope that helps.
Rich
Rich Alderson
Vintage Computing Sr. Systems Engineer
Living Computers: Museum + Labs
2245 1st Avenue S
Seattle, WA 98134
mailto:RichA at LivingComputers.org
http://www.LivingComputers.org/