14 Dec
2020
14 Dec
'20
1:26 a.m.
Often for data input one could use over strike characters for input. Not
EQ might be = BS | Did any video display terminals
repeat the same effect?
Ben.
14 Dec
14 Dec
2:41 a.m.
On 2020-Dec-14, at 1:26 AM, ben via cctalk wrote:
Often for data input one could use over strike
characters for input. Not EQ might be = BS | Did any video display terminals
repeat the same effect?
Yes. Coincidentally I've just been refurbishing one - a Teleray 3931.
It's an ASCII/APL terminal, overstriking was included for the APL mode.
http://madrona.ca/e/teleray3931/index.html
Note the screenshots in APL mode.
6:26 a.m.
On 2020-12-14 05:41, Brent Hilpert via cctalk wrote:
On 2020-Dec-14, at 1:26 AM, ben via cctalk wrote:
Is it really an overstrike? They look simply like different characters.
At least, I didn't (probably missed it) how they can be generated out of
the available ones...
Often for data input one could use over strike
characters for input. Not EQ might be = BS | Did any video display terminals
repeat the same effect?
Yes. Coincidentally I've just been refurbishing one - a Teleray 3931.
It's an ASCII/APL terminal, overstriking was included for the APL mode.
http://madrona.ca/e/teleray3931/index.html
Note the screenshots in APL mode. 
6:28 a.m.
On Dec 14, 2020, at 9:26 AM, emanuel stiebler via
cctalk <cctalk at classiccmp.org> wrote:
On 2020-12-14 05:41, Brent Hilpert via cctalk wrote:
I wondered too. General overstrike requires a bitmap display, or some sort of persistent
display. Paper is an example; a Tek 4010 would also handle overstrike since it uses a
storage tube. And PLATO terminals did overstrike just fine since they are bitmap displays
with per-pixel memory.
paul
On 2020-Dec-14, at 1:26 AM, ben via cctalk
wrote:
Is it really an overstrike? They look simply like different characters.
At least, I didn't (probably missed it) how they can be generated out of
the available ones... Often for data input one could use over strike
characters for input. Not EQ might be = BS | Did any video display terminals
repeat the same effect?
Yes. Coincidentally I've just been refurbishing one - a Teleray 3931.
It's an ASCII/APL terminal, overstriking was included for the APL mode.
http://madrona.ca/e/teleray3931/index.html
Note the screenshots in APL mode. 
8:51 a.m.
On 12/14/20 6:28 AM, Paul Koning via cctalk wrote:
Back in the day (why is everything now "back in the day"?), I wrote the
firmware for a Fortune Systems text terminal. The requirement was for a
certain degree of NAPLPS/Videotex compatibility. Combining certain
characters was done via lookup in the character generator ROM, not by
combining them as graphical characters. I suspect that this was the
method used for a large number of terminals, such as the Telidon units.
--Chuck
Is it really
an overstrike? They look simply like different characters.
At least, I didn't (probably missed it) how they can be generated out of
the available ones...
I wondered too. General overstrike requires a bitmap display, or some sort of persistent
display. Paper is an example; a Tek 4010 would also handle overstrike since it uses a
storage tube. And PLATO terminals did overstrike just fine since they are bitmap displays
with per-pixel memory.
1:38 p.m.
On 2020-Dec-14, at 6:28 AM, Paul Koning wrote:
Yes, it really is overstrike. This is pretty much explained in the text. You generate
overstrikes by backing up and entering a 2nd character.
There are two full screen buffers, but only one page of display. There is a spring-loaded
3-position switch that allows you to temporarily 'disable' either of the buffers,
so that only the characters in the other buffer are on screen while you hold the switch.
There are 95 symbols in the APL set encoded in the range 0x20 to 7E, as shown on the
screenshots.
Now I haven't tried all 9025 possible overstrike combinations, but all sorts of
non-sensical combinations produce what would be the expected result - an OR of the pixels
of the contributing characters. For example, "A" can be overstruck with all the
other letters of the alphabet, and all the letters of the alphabet can be overstruck with
"A". It's not just the valid APL overstrike combinations.
A general overstrike capability like this doesn't need a bitmap display to accomplish.
I haven't RE'd the character-pixel generation section, but the ICs present and the
behaviour points to it doing something along the lines of:
In raster scanning, for each screen character cell:
- address buffer 1, send code through character generator, store result in pixel shift
register.
- address buffer 2, send code through character generator, OR result into pixel shift
register.
- shift the shift register pixels out to CRT.
- repeat for next character cell
On Dec 14,
2020, at 9:26 AM, emanuel stiebler via cctalk <cctalk at classiccmp.org> wrote:
On 2020-12-14 05:41, Brent Hilpert via cctalk wrote:
I wondered too. General overstrike requires a bitmap display, or some sort of persistent
display. Paper is an example; a Tek 4010 would also handle overstrike since it uses a
storage tube. And PLATO terminals did overstrike just fine since they are bitmap displays
with per-pixel memory. On 2020-Dec-14, at 1:26 AM, ben via cctalk
wrote:
Is it really an overstrike? They look simply like different characters.
At least, I didn't (probably missed it) how they can be generated out of
the available ones... Often for data input one could use over strike
characters for input. Not EQ might be = BS | Did any video display terminals
repeat the same effect?
Yes. Coincidentally I've just been refurbishing one - a Teleray 3931.
It's an ASCII/APL terminal, overstriking was included for the APL mode.
http://madrona.ca/e/teleray3931/index.html
Note the screenshots in APL mode. 
7:57 a.m.
On 12/14/20 4:41 AM, Brent Hilpert via cctalk wrote:
On 2020-Dec-14, at 1:26 AM, ben via cctalk wrote:
Holy cow, I have that keyboard. I picked it up as surplus a few years ago
Often for data input one could use over strike
characters for input. Not EQ might be = BS | Did any video display terminals
repeat the same effect?
Yes. Coincidentally I've just been refurbishing one - a Teleray 3931.
It's an ASCII/APL terminal, overstriking was included for the APL mode.
http://madrona.ca/e/teleray3931/index.html from a place in Minneapolis and figured there was a
very low probability of
ever figuring out what machine it originally came from.
I didn't know the necessary voltages for it - I mean, the grounds and +5V
are obvious, but I didn't know what it needed on pin 6. Given where I got
it from, there's probably a fair chance that it's faulty (and encoders
generally live a hard life), but I'll have to try powering it up now.
Just FYI if you're documenting things, mine has a very slightly different
PCB to accommodate a pair of tantalum caps on the inputs, rather than the
electrolytics on yours - caps are both rated 10uF, 35V. The encoder on mine
is the same p/n but in a black plastic package rather than white ceramic
(date code 7649). Sticker on the PCB underside says p/n 2129-009 and s/n
720 097.
(It's definitely -12V, not -5V? I'm just thinking that the -12V noted on
your schematic is quite close the the 15V rating on the cap - although that
could explain why my later setup got caps rated to 35V, too)
cheers!
Jules
8:06 p.m.
On 2020-Dec-14, at 7:57 AM, Jules Richardson wrote:
On 12/14/20 4:41 AM, Brent Hilpert via cctalk wrote:
...
Yes. Coincidentally I've just been refurbishing one - a Teleray 3931.
It's an ASCII/APL terminal, overstriking was included for the APL mode.
http://madrona.ca/e/teleray3931/index.html
Holy cow, I have that keyboard. (It's definitely -12V, not -5V? I'm just
thinking that the -12V noted on your schematic is quite close the the 15V rating on the
cap - although that could explain why my later setup got caps rated to 35V, too)
I don't remember whether I traced it or measured it, but I'm fairy confident, Vgg
= -12 is pretty common for GI MOS ICs.
I'll try to remember to double-check it when I have the unit opened again.
I have some other orphan keyboard of the period, don't recall which scanner IC it
uses, but it has the similar +Vcc/-Vgg requirement.
I made up a little negative supply with a 7660 charge pump and tacked it onto the keyboard
PCB so the keyboard now only needs +5 externally.
15 Dec
15 Dec
11:15 a.m.
On 12/14/20 10:06 PM, Brent Hilpert via cctalk wrote:
Thanks! I guess I can try it first on -5V too and see if the encoder
outputs do anything, and if not give -12V a go. If it works, I like the
charge pump idea - I'd probably ultimately give it its own case and use it
externally, so saving a wire is handy.
cheers
Jules
(It's
definitely -12V, not -5V? I'm just thinking that the -12V noted
on your schematic is quite close the the 15V rating on the cap -
although that could explain why my later setup got caps rated to 35V,
too)
I don't remember whether I traced it or measured it, but I'm fairy
confident, Vgg = -12 is pretty common for GI MOS ICs. I'll try to
remember to double-check it when I have the unit opened again.
1:49 p.m.
On 2020-Dec-15, at 11:15 AM, Jules Richardson via cctalk wrote:
On 12/14/20 10:06 PM, Brent Hilpert via cctalk wrote:
Thanks! I guess I can try it first on -5V too and see if the encoder outputs do anything,
and if not give -12V a go. If it works, I like the charge pump idea - I'd probably
ultimately give it its own case and use it externally, so saving a wire is handy.
Just double-checked by measurement, yes, it is -12V.
(It's
definitely -12V, not -5V? I'm just thinking that the -12V noted
on your schematic is quite close the the 15V rating on the cap -
although that could explain why my later setup got caps rated to 35V,
too)
I don't remember whether I traced it or measured it, but I'm fairy
confident, Vgg = -12 is pretty common for GI MOS ICs. I'll try to
remember to double-check it when I have the unit opened again.
21 Dec
21 Dec
4:11 p.m.
On 12/14/20 10:06 PM, Brent Hilpert via cctalk wrote:
On 2020-Dec-14, at 7:57 AM, Jules Richardson wrote:
Hey,
Just a heads-up, I finally got around to hooking it up - and it works just
fine on -5V. I'm not inclined to try -12V just in case it cooks, but I
suppose it's possible that it just needs some -ve voltage "more than x" and
so -12V is perfectly acceptable, too. Or maybe I just got lucky and this IC
is happy on -5V where some might not be.
I'm pretty happy that it's alive, anyway. I need to figure out what's going
on with the spacebar (it currently doesn't sit level), but time to figure
out some frankenproject for it!
cheers
Jules
On 12/14/20 4:41 AM, Brent Hilpert via cctalk
wrote:
...
Yes. Coincidentally I've just been refurbishing one - a Teleray
3931. It's an ASCII/APL terminal, overstriking was included for the
APL mode. http://madrona.ca/e/teleray3931/index.html
Holy cow, I have that keyboard. (It's definitely -12V, not -5V? I'm just
thinking that the -12V noted
on your schematic is quite close the the 15V rating on the cap -
although that could explain why my later setup got caps rated to 35V,
too)
I don't remember whether I traced it or measured it, but I'm fairy
confident, Vgg = -12 is pretty common for GI MOS ICs. I'll try to
remember to double-check it when I have the unit opened again. 
1414
days inactive
1422
days old
11 comments
7 participants
participants (7)
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bfranchuk＠jetnet.ab.ca -
bhilpert＠shaw.ca -
bill.gunshannon＠hotmail.com -
cclist＠sydex.com -
emu＠e-bbes.com -
jules.richardson99＠gmail.com -
paulkoning＠comcast.net