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List:       classiccmp
Subject:    CDC 6000 series transistors [was RE: Which Dec Emulation is the MOST useful and Versatile?]
From:       Rich Alderson via cctalk <cctalk () classiccmp ! org>
Date:       2017-10-30 20:13:52
Message-ID: bf2f1c3ab9294dceac504218eaf7e964 () livingcomputers ! org
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From: Paul Koning
Sent: Friday, October 27, 2017 12:07 PM

> True if you have a TTL machine.  6600 is discrete transistor, and the act=
ual
> transistor specs are nowhere to be found as far as I have been able to te=
ll.

> But that doesn't directly relate to gate level emulation.  If you have ga=
te
> 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 m=
odel
> in VHDL, which is not the most popular form but certainly perfectly
> straightforward.  Either way, though, you have to start with a document t=
hat
> shows what the gates are in the original and how they connect.  And to ge=
t 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 bee=
n
> debugging a section (the central processor branch logic) where the behavi=
or
> 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 cir=
cuit
> 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 shor=
ter
    version of the to-18 package. I have had good success with both the 2n2=
369
    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 r=
eset
    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 ar=
row
    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 1=
20
    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@LivingComputers.org

http://www.LivingComputers.org/
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