Foone🏳️⚧️
so I'm looking into how the keyboard for the Wyse-50 dumb terminal works, and it turns out there's no protocol, no smarts.
Instead they use a 12-pin (11 pin?) connector, and the keyboard has two LS156 demultiplexers, and a CD4051 multiplexer/demultiplexer.
So what they do is scan the keyboard matrix, like any keyboard IC does... except the main CPU is doing it, not the keyboard's smarts (since it has none)
Foone🏳️⚧️
that's an unusual design for a system which has an external keyboard that has a removable plug!
Foone🏳️⚧️
ANYWAY it turns out I don't need to care about how the Wyse-50 did the keyboard: The two Wyse terminals I'm having to interface with are a 30 and 60, not a 50.
And while the 30 and 60 both switched to having a custom IC that encodes some kind of 4-wire serial protocol (seems to be a shift-register?), I can't be sure that they're remotely compatible, because the keyboards are different.
Foone🏳️⚧️
okay so I found a fun thing with my Wyse-60 when I hooked it up to a serial port: Some of the letters are showing up corrupted. But here's the fun part: It's not corruption based on which symbol it is, but on where on screen (or in buffer) they are.
It seems to be switching to a larger font, but it's on that's too big for the character cell size.
Foone🏳️⚧️
so I found a character (period) that's visible normally but not when gibberished, and filled the screen with it.
ta-da! I now have a visual map of where the memory is corrupted.
Foone🏳️⚧️
An interesting thing is that when the screen scrolls, so do the corrupted sections.
So I guess that means the bad RAM isn't in the screen VRAM, but it's in the RAM of the scrollback buffer
Foone🏳️⚧️
also apparently my Wyse-60 terminal was originally used by Lucasfilm. Sprockets is what became Skywalker Sound.
Foone🏳️⚧️
So the age of this terminal and the name dates this to 1986-1989. So the films Sprocket Systems were working on were:
Willow, Tucker, The Abyss, and Indiana Jones and the Last Crusade
Foone🏳️⚧️
It's probably not a good sign when the maintenance manual lists the danger radius.
In this case, six to ten feet.
Foone🏳️⚧️
@artandtechnic six to ten feet of IMPLODING GLASS!
Glyph
@foone I think I listened to a lot of MC Ten Foot Danger Radius in college
Foone🏳️⚧️
@glyph their albums couldn't be released in the EU due to regulations, so they had to go by the name MC 3.05 Meter Danger Radius
Foone🏳️⚧️
@jazzoomazzoo it's a CRT: they're talking about how far the glass chunks might go flying
Mazzy
@foone ???
Is this like, a gross misapplication of NEC prohibited approach boundary for live circuits, or something far stranger?
Foone🏳️⚧️
@jazzoomazzoo this isn't the caps, it's nothing electrical. It's just the tube itself imploding
Mazzy
@foone okay I knew the capacitors in CRTs were not to be trifled with but DAMN
Foone🏳️⚧️
my wife suggested I get a ten-foot-pole with which to touch this machine
Foone🏳️⚧️
good news: I got it out. No exploding.
Foone🏳️⚧️
Here's the main CPU: A socketed Signetics 8051.
Foone🏳️⚧️
Here's the firmware. An ST M27512FI 64 kilobyte EPROM.
Wyse Tech 89' Rev A
Foone🏳️⚧️
MC68661PB: This is an Enhanced Programmable Communication Interface, one specifically designed for interfacing to the MC68000. Weird. This is designed for 16bit computers, and this is an 8-bit?
Foone🏳️⚧️
This WYSE 211003-02 is apparently the video chip. Interesting that it's custom. I'd expect them to just stick a Motorola 6847 in there.
Foone🏳️⚧️
while I'm in here, I'm gonna need to fix this cap that seems to have exploded.
Foone🏳️⚧️
So this thing has a bunch of ram in different places.
Apparently this M5M5165P at U19 is 8 kilobytes of font ram.
Foone🏳️⚧️
Over here at U8 is another M5M5165P, which is 8 kilobytes of general RAM
Foone🏳️⚧️
And at U15 and U16 are these weird Avasem/Wyse 192017-02 chips. I think I think these are custom 2 kilobyte RAM chips?
I don't know why they'd be custom. That's especially bad because I think these are what broke.
Foone🏳️⚧️
And another M5M5165 at U7, which is the Char RAM (another 8 kilobytes)
Foone🏳️⚧️
so I think I'm gonna wait until I get in my keyboard (tomorrow!) and then try to make this thing run a self-test. Maybe it can tell me which chips are broken.
Foone🏳️⚧️
you can enable self-test by putting a jumper on the serial and aux ports, but you also have to press some keys on the keyboard, so if your keyboard is broken (or missing), you can't test it.
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