tty and video displays

Chuck Guzis cclist at
Mon Dec 14 10:51:48 CST 2020

On 12/14/20 6:28 AM, Paul Koning 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...
> 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.

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.


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