back to the AGC, was Re: TTL 7400's Available

[Allison]

>
>Subject: back to the AGC, was Re: TTL 7400's Available
>   From: Brent Hilpert <hilpert at cs.ubc.ca>
>   Date: Tue, 02 Jan 2007 20:24:39 -0800
>     To: General at priv-edtnaa05.telusplanet.net,
> "Discussion at priv-edtnaa05.telusplanet.net":On-Topic and Off-Topic Posts
> <cctalk at classiccmp.org>
>
>Chuck Guzis wrote:
>> 
>> I stumbled on this document:
>> 
>> http://klabs.org/mapld04/papers/g/g233_alonso_p.doc
>> 
>> while wondering about AC transformer-coupled logic and discovered
>> that the original idea for the Apollo guidance computer was to use AC-
>> coupled (core-transistor) logic.
>> 
>> How's that for tying two threads together? :)
>
>Now that was a fun read. I'm still trying to understand his description of
>the core rope ROM though. I'm familiar with core-rope ROM (or at least one
>version of it) from attempting to make a reader to dump the contents of a Wang
>calc microcode ROM, but the AGC version sounds like the
>address-decoding/word-selection is done differently (..need a diagram).

cant help on core rope.

>And whats up with this mention of LCD displays? I didn't think there was
>anything practical available that early, or that was going to stand up to the
>rigours of space-flight - I have a calc with one of the first commercial LCDs
>(1972) and it's still kind of rudimentary - slow, poor contrast, temperature sensitive...

My memory of LCDs is they were way too late for the AGC and the basic
AGC design used either LEDs or Lamps in a 7 segment format.

>(And it confirmed that the AGC was constructed from a single gate/IC type.)

That statement I believe is in error.  While the logic used was RTL and a 
single family type the logic elements for that family by the mid 60s were 
more diverse than just a two input NOR. My junkbox contains parts from 
the era and includes JK-FF, three input nor, inverter buffers, and three 
wide NOR parts.  It is true that the 2input NOR is the fundamental RTL 
logic building block there was nothing to limit it to 2,3 or 4 inputs 
for the die size of the time other than the hermetic flat packs of 
the day were typically 8/10/12 pins.

Examples of mid 60s RTL.

  ul900 buffer inverter
  uL914 dual two input nor
  uL923 jk-ff
  uL925 dual 2 input nor gate expander (914 withput collector resistor).

These were widely available and purchaseable by hobbists in 1967
at reasonable prices, typically under $2.00US.  Most ham/electronics
magazines had DMM and frequency counter projects using these parts
by or during 1968.

History of transistor computers by that time frame had already proven 
that a minimal set of logic blocks made general computer design easier.
The TX1 and TX2 could stand as foundation machines on that basis alone. 
Those bocks were an inverter(buffer), NOR or NAND, and a register (FF). 
Any more specialized parts were likely used for core or other very limited 
use parts of a computer.

RTL is old, some of the peices I have are now reaching 40!


Allison