🚀 go-pugleaf

It looks to me as though the voltage level and impedance out of the "composite
luminance" port of the 800XL should be about right to drive a TTL logic input,
for what that's worth.  At most, this would require one "comparator" IC to
make sure the levels are right.

Luminance is on Pin 1 of the 800XL jack, which, however, may not be where you
would think Pin 1 would be placed!

I am not familiar with what TTL monitors look like, so I can't give you a
definitive answer.  If it just looks for a single binary TTL level input, the
above comments are about all you need. If it is a mult-bit digital input then
you will need some kind of A/D converter if you want gray levels.  If you are
just doing word processing or otherwise can afford just two levels (black and
amber or whatever) then you could run the single bit from Pin 1, either
through a comparator/level converter or not, and run it through an inverter so
you can turn it into two patterns with high contrast between them like
01111111 and 10000000.

I hope this is of some help.  Good luck with the project.

-John Sangster,
jhs@mitre-bedford.arpa