gathings@cs.utk.edu (Golando Gathings) (06/10/91)
I am looking for a little ckt that will take the ttl levels of either a mono or color card of a pc compatible and convert it to a composite signal. I have seen it done before , but I do not have the refs with me at this time. All replies are welcome. Thanks Golando
cgordon@vpnet.chi.il.us (gordon hlavenka) (06/10/91)
In article <1991Jun9.235022.20505@cs.utk.edu> gathings@cs.utk.edu (Golando Gathings) writes: > I am looking for a little ckt that will take the ttl >levels of either a mono or color card of a pc compatible and convert >it to a composite signal. I have here a thing called the "Missing Link". It's an oldie, perhaps out of production. It has a DB-9 on one end, and an RCA jack on the other. You plug it on the RGB output of a CGA card, and it makes composite video. There's nothing in it but resistors; email me if you want specifics. The address on the package: Active Components 4000 W. Clearwater Ave. Kennewick, WA 99336 (509) 783-5065 This gizmo will produce grayscale BW video. If you can dig into a CGA card, you should be able to cobble up a burst and get color. (Actually, every CGA I've seen has had a composite output...) Incidentally, know why the original PC ran at 4.77 MHz? Because they could use a crystal timebase running at 14.318180 Mhz and divide it by 3 (the 8284 clock driver does /3) to get something less than 5 MHz, the spec on cheap 8088s. If you divide that same crystal by 4 you get... If they'd used a 15Mhz rock for the 8284, they'd have had to spend an extra 50 cents on every CGA card to put a burst crystal on it. I don't know of a way to get composite from an MDA/Herc card without proc- essing; the scan freqs are all wrong for NTSC. -- ----------------------------------------------------- Gordon S. Hlavenka cgordon@vpnet.chi.il.us Disclaimer: Yeah, I said it. So what?
mzenier@polari.UUCP (Mark Zenier) (06/12/91)
In article <1991Jun9.235022.20505@cs.utk.edu> gathings@cs.utk.edu (Golando Gathings) writes: > > I am looking for a little ckt that will take the ttl >levels of either a mono or color card of a pc compatible and convert >it to a composite signal. I have seen it done before , but I do >not have the refs with me at this time. All replies are welcome. 1. Radio-Electronics December 1989 2. Circuit Cellar Ink, Issue #1 and #2 3. Motorola Application note AN-932, "Application of the MC1377 color encoder" The special delay lines and coil used to be listed as a seperate category in the TOKO section of the Digi-Key catalog. They may still carry them. Remember that the horizontal line period has to be 63.555 microseconds and the vertical period has to be 16.683 milliseconds for any NTSC equipment to come close to accepting the output. This rules out mono and hercules cards. Mark Zenier markz@ssc.uucp mzenier@polari.uucp