> On Jul 1, 2019, at 8:11 PM, Bob Supnik <[email protected]> wrote:
>
> The PLA scheme (another invention from the fertile mind of Bill Roberts,
> architect of the LSI11 and UDA50 proto and founder of Emulex) was basically a
> microcode and gate conservation scheme. It provided enormous compression for
> the decode phase of the PDP11 and then got exploited to a fare-thee-well by
> clever microcoders like Burt Hashizume (F11) and Keith Henry (J11).
Using logic to represent what you might think of as a table of values (a ROM)
appears in other places too. The CDC 6000 series console display, from 1964,
has tables of stroke data. Those are documented as lists of 5 bit data, up to
23 rows for each character, 45 character codes total.
In the later 170 series controller this is indeed done in a ROM, but the 6000
series controller used discrete transistor logic and a ROM wasn't a possible
option then (not when a new value was needed every 100 ns). So instead it uses
a rather large tree of gate logic to produce the data. Large as in roughly 130
"cordwood" plug-in modules, each with 30 or so transistors on them.
paul
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