4 May
2021
4 May
'21
2:33 a.m.
I'm currently reverse-engineering an AMPEX keyboard that uses capacitive key
switches. The basic design employs a GI encoder coupled to an 8039 MCU
supplemented by a 2K EPROM and 74LS373 (used to latch the ROM address set
from Port A while Port A is then used to read data back
from the ROM). The
8039 MCU drives a bit-banged serial interface. The PCB
identifies itself as
AMPEX on the coper foil, although the key switch mounting-plate actually has
a "General Instruments Quality Accepted" sticker. The EPROM is labeled
"3512663-03 Copyright 1983 AMPEX CORP".
The GI encoder is a DIP-40 labeled as "321239007 M2406-054-02 GI 8233 CBU
TAIWAN". I seek technical documentation for this IC.
It evidently is not a relabeled simple variant of the documented AY-3-4592
as it does not multiplex the input side of the matrix (sense lines), there
are fewer output data lines, and the power pins are non-standard (Vcc = pin
37; GND = pin 16).
Reverse engineering identifies this M2406-054-02 as supporting an 8 column
by 16 row (3 unused in my case) matrix plus 8 output data lines. I can
identify analogs of several pins on the AY-3-4592. My interpretation of the
pin uses is that the necessary key-scanning behavior is generated using the
8039 ALE line (pin 11) as the encoder clock input.
Proper documentation for this IC would be nice to come by! Pointers and
suggestions appreciated.
Thank you,
paul
7:18 a.m.
-----Original Message-----
From: cctalk [mailto:cctalk-bounces at classiccmp.org] On Behalf Of Al Kossow via cctalk
Sent: Tuesday, May 04, 2021 9:48 AM
To: cctalk at classiccmp.org
Subject: Re: General Instruments Capacitive Keyboard Encoder
On 5/4/21 2:33 AM, Paul Birkel via cctalk wrote:
It uses individual sprung metal leaves, with the exception of the caps-lock key which has
a central LED and around that an annular square foil/pad that is in fine shape. It's
all nicely constructed; the case even includes a spray-on metallized surface that is
connected via a sprung contact to the cable shield and the switch-body retaining plate.
-----
I'm currently reverse-engineering an AMPEX
keyboard that uses capacitive key
switches.
did all of the square foil and foam pads disintegrate in it? 
7:46 a.m.
On Tue, May 4, 2021 at 10:33 AM Paul Birkel via cctalk
<cctalk at classiccmp.org> wrote:
I'm currently reverse-engineering an AMPEX keyboard that uses capacitive key
switches. The basic design employs a GI encoder coupled to an 8039 MCU
supplemented by a 2K EPROM and 74LS373 (used to latch the ROM address set
from Port A while Port A is then used to read data back from the ROM). The
8039 MCU drives a bit-banged serial interface. The PCB identifies itself as
AMPEX on the coper foil, although the key switch mounting-plate actually has
a "General Instruments Quality Accepted" sticker. The EPROM is labeled
"3512663-03 Copyright 1983 AMPEX CORP".
The GI encoder is a DIP-40 labeled as "321239007 M2406-054-02 GI 8233 CBU
TAIWAN". I seek technical documentation for this IC.
You might take a look at the manuals here :
http://cpu-ns32k.net/Whitechapel.html
I am pretty sure there's a keyboard techincal description in 'binder
1' and a reverse-engineered schematic in 'binder 2'. While it's not
quite the same IC, it's related and the power pins are in the right
place :-)
Alas there is no real description of what that IC does or how to talk
to it from the 8039. It is designed to sit on the 8039 bus, it takes
in the multiplexed address/data bus, ALE, rd/ and wr/
-tony
5 May
5 May
12:12 a.m.
-----Original Message-----
From: Tony Duell [mailto:ard.p850ug1 at gmail.com]
Bingo. That's basically my circuit here (pin for pin) with minor differences in RC
values and a much more interesting serial interface (and a _four_ finger salute no less!
N-S-T-V Take that DOS ...), although mine supports a buzzer/speaker.
The principal inconsistency is that pin 25 is marked "CS" and left open in the
"binder 1" schematic (page 132 of 134), and then doesn't appear in your
hand-drawn schematic (page 7 of 24). In my circuit it's wired to the 8039 ~PSEN.
The straight-thru wiring on ~RD and ~WR alongside ALE with no address decoding is IMO
rather odd. I wonder how that design actually works (either assumes that it is the only
writable device present, or actually latches 8 bits of address and shadows some valid ROM
address) and then what gets written to the encoder for what purpos(es). Disassembly of the
EPROM should answer those questions. My objective here is to replace the bit-banged
interface with a parallel interface emulating one for an Intel MDS-230.
Two questions on notation.:
1. In the "binder 1" schematic pin 6 is marked as R<sub>y and is pulled up
via resistor to +5v. On your hand-drawn schematic the corresponding pin appears to be
labeled "PVR". What might be the function of this pin?
2. In the "binder 1" schematic pin 15 is marked as C<sub>m and is attached
to an RC circuit. On your hand-drawn schematic the corresponding pin appears to be
labeled "RC". C = 100 nF. What might be the function of this pin? I'm
guessing ~(Power On Reset) rather than as the basis for an on-chip oscillator as seen in
the AY-3-4592 pin 36 "RC" given the relatively high capacitance value.
Thank you for these new breadcrumbs.
paul
On Tue, May 4, 2021 at 10:33 AM Paul Birkel via
cctalk <cctalk at classiccmp.org> wrote:
I'm currently reverse-engineering an AMPEX keyboard that uses capacitive key
switches. The basic design employs a GI encoder coupled to an 8039 MCU
supplemented by a 2K EPROM and 74LS373 (used to latch the ROM address set
from Port A while Port A is then used to read data back from the ROM). The
8039 MCU drives a bit-banged serial interface. ...
The GI encoder is a DIP-40 labeled as "321239007 M2406-054-02 GI 8233 CBU
TAIWAN". I seek technical documentation for this IC.
You might take a look at the manuals here :
http://cpu-ns32k.net/Whitechapel.html
I am pretty sure there's a keyboard techincal description in 'binder
1' and a reverse-engineered schematic in 'binder 2'. While it's not
quite the same IC, it's related and the power pins are in the right
place :-)
Alas there is no real description of what that IC does or how to talk
to it from the 8039. It is designed to sit on the 8039 bus, it takes
in the multiplexed address/data bus, ALE, rd/ and wr/
12:36 a.m.
On Wed, May 5, 2021 at 8:12 AM Paul Birkel <pbirkel at gmail.com> wrote:
Remember that the 8039 has separate program and data memory spaces.
PSEN/ (Program Store ENable) is asserted to access the ROM .If pin 25
of the keyboard scanner chip is CS, that might be Chip Select (active
high), to ensure the chip is disabled on ROM accesses.
Rd/ and Wr/ are asserted to access data memory. Here the only device
is the keyboard scanner chip, so there's no need for address decoding.
Since the keyboard scanner chip takes in ALE, there's a chance it uses
the lower 8 address lines (multiplexed with the data bus) to select
different internal registers,
-----Original Message-----
From: Tony Duell [mailto:ard.p850ug1 at gmail.com]
Bingo. That's basically my circuit here (pin for pin) with minor differences in RC
values and a much more interesting serial interface (and a _four_ finger salute no less!
N-S-T-V Take that DOS ...), although mine supports a buzzer/speaker.
The principal inconsistency is that pin 25 is marked "CS" and left open in the
"binder 1" schematic (page 132 of 134), and then doesn't appear in your
hand-drawn schematic (page 7 of 24). In my circuit it's wired to the 8039 ~PSEN.
The straight-thru wiring on ~RD and ~WR alongside ALE with no address decoding is IMO
rather odd. I wonder how that design actually works (either assumes that it is the only
writable device present, or actually latches 8 bits of address and shadows some valid ROM
address) and then what gets written to the encoder for what purpos(es). Disassembly of the
EPROM should answer those questions. My objective here is to replace the bit-banged
interface with a parallel interface emulating one for an Intel MDS-230. On Tue, May 4, 2021 at 10:33 AM Paul Birkel via
cctalk <cctalk at classiccmp.org> wrote:
I'm currently reverse-engineering an AMPEX keyboard that uses capacitive key
switches. The basic design employs a GI encoder coupled to an 8039 MCU
supplemented by a 2K EPROM and 74LS373 (used to latch the ROM address set
from Port A while Port A is then used to read data back from the ROM). The
8039 MCU drives a bit-banged serial interface. ...
The GI encoder is a DIP-40 labeled as "321239007 M2406-054-02 GI 8233 CBU
TAIWAN". I seek technical documentation for this IC.
You might take a look at the manuals here :
http://cpu-ns32k.net/Whitechapel.html
I am pretty sure there's a keyboard techincal description in 'binder
1' and a reverse-engineered schematic in 'binder 2'. While it's not
quite the same IC, it's related and the power pins are in the right
place :-)
Alas there is no real description of what that IC does or how to talk
to it from the 8039. It is designed to sit on the 8039 bus, it takes
in the multiplexed address/data bus, ALE, rd/ and wr/
Two questions on notation.:
1. In the "binder 1" schematic pin 6 is marked as R<sub>y and is pulled
up via resistor to +5v. On your hand-drawn schematic the corresponding pin appears to be
labeled "PVR". What might be the function of this pin?
2. In the "binder 1" schematic pin 15 is marked as C<sub>m and is
attached to an RC circuit. On your hand-drawn schematic the corresponding pin appears to
be labeled "RC". C = 100 nF. What might be the function of this pin? I'm
guessing ~(Power On Reset) rather than as the basis for an on-chip oscillator as seen in
the AY-3-4592 pin 36 "RC" given the relatively high capacitance value.
My guess is that I called the first 'PUR' for pull-up resistor :-) It
may actually set the sensitivity of the row inputs or somethng.
The second may be an RC delay to allow the keyboard to settle. There's
something similar in the PERQ2 keyboard which uses separate row and
column chips.
-tony
1:03 a.m.
-----Original Message-----
From: Tony Duell [mailto:ard.p850ug1 at gmail.com]
On Wed, May 5, 2021 at 8:12 AM Paul Birkel <pbirkel at gmail.com> wrote:
Remember that the 8039 has separate program and data memory spaces.
"Sokath, his eyes uncovered." Thank you Tony. Your notation observations both
sound very reasonable to me.
paul
-----Original Message-----
From: Tony Duell [mailto:ard.p850ug1 at gmail.com]
The straight-thru wiring on ~RD and ~WR alongside ALE with no address decoding is IMO
rather odd. I wonder how that design actually works (either assumes that it is the only
writable
device present, or actually latches 8 bits of address and shadows some valid ROM address)
and then what gets written to the encoder for what purpos(es). On Tue, May 4, 2021 at 10:33 AM Paul Birkel via
cctalk <cctalk at classiccmp.org> wrote:
The GI encoder is a DIP-40 labeled as "321239007 M2406-054-02 GI 8233 CBU
TAIWAN". I seek technical documentation for this IC.
You might take a look at the manuals here :
http://cpu-ns32k.net/Whitechapel.html
I am pretty sure there's a keyboard techincal description in 'binder
1' and a reverse-engineered schematic in 'binder 2'. While it's not
quite the same IC, it's related and the power pins are in the right
place :-)
Alas there is no real description of what that IC does or how to talk
to it from the 8039. It is designed to sit on the 8039 bus, it takes
in the multiplexed address/data bus, ALE, rd/ and wr/
1108
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6 comments
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