Help identifying Mystery CDC Terminal...

Brent Hilpert hilpert at
Sun Feb 17 23:16:23 CST 2008

Josh Dersch wrote:
> There's some bad
> RAM (assuming this thing uses RAM), though -- a couple of character
> cells show up incorrectly (dropping the lowest two bits).  And by "a
> couple" I mean exactly two :).  The display needs a few capacitors
> replaced, but the picture's still very good given the age.

If you're not familiar with terminals of this vintage, aside from the 14/16 pin
SSI/MSI ICs in there, you'll likely find a MOS character generator ROM
(probably the only large (>16 pin) chip). The memory would typically be early
MOS shift register chips (although the symptoms you describe suggest addressed
mem) or early MOS DRAM.

> The terminal seems to provide an 80x16 character display of both upper
> and lower-case letters. 
> It has some sort of memory expansion option
> installed, according to tags in the case... I have no idea what extra
> functionality that gives it.

Likely a second page/screen of 80*16, how to switch between them will be the
question, might be keys/switches or it might be control characters like DCx, or FF.

BTW, beyond the displayable characters, screen manipulation is likely limited
to what can be accomplished with the ASCII control characters. Check out what
FF,VT,HT,BS,&c. do. (Like this one, *real* terminals have the control codes 
imprinted on the keys.) (Although I'll certainly defer to somebody who may kno
CDC better and whether they had some internal standard for terminal control perhaps.)

> There's also a huge empty space below the
> monitor/cardcage/power supply which seems to have been meant for some
> additional expansion options, it'd be interesting to know what those were...

That sounds familiar, that's where another guy in the school stuffed in the MEK
6800 board and hacked it into the power supply and RS232 line. (I confess I
didn't really like it, even then I wasn't fond of hacking up original, intact, equipment.)

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