mmm@cup.portal.com (Mark Robert Thorson) (05/24/90)
To correct any misinterpretations of the previous post, I'd just like to point out that the interlace is generated in the source of the video signal, by adding a half-line at the end of the frame. This shifts the next frame by a half-line in the vertical dimension. Your monitor's selection between interlaced and non-interlaced modes probably just changes the speed of the sync pulses the monitor is expecting. The original poster wanted to run a signal from a VCR into a video monitor from an ASCII terminal. This is possible, but not trivial. The cheap video monitor in the terminal requires a sync signal. To get this from a composite signal, you need a sync separator. There must be one in the VCR, so it may be possible to find a suitable signal in there. So maybe you could connect the composite signal to the video input, and probe around inside the VCR with the sync input. As I've described in the past in this group, I once modified a TV set to receive pay-TV signals encoded using inverted sync by a similar means. I located a trace on the circuit board which appeared to connect the video section to the sweep circuits. I cut the trace, and turned the TV on, and the picture would roll asynchronously to the transmitted picture. Then, I hooked the suspected horz sync signal to various places in earlier stages of the video section, until I found an inverted sync signal. Then, I wired in a switch to flip back and forth between normal and inverted sync pulses. Be warned that the voltage levels might not be compatible. Also, a TTL input on the monitor might be too much load for a CMOS output in the VCR.
markz@ssc.UUCP (Mark Zenier) (05/25/90)
In article <24431@unix.cis.pitt.edu>, fmgst@unix.cis.pitt.edu (Filip Gieszczykiewicz) writes: > Greetings. I have a VCR with a COMPOSITE output that I > want to use. I also have a _large_ number of terminals > that lack the "digital" sections but have the CRT drive > circuits in "prime" condition. Is it possible to use > it with COMPOSITE? How? Specifically, I have a couple > Visual 90s and some Televideo 912Cs that I would like to > make something of... Anyone done it before? Here's the pinout that seems to be standard for open frame TTL drive monitors. 01 ground 02 contrast pot, one end (50k ohm ?) 03 contrast pot, the other end 04 contrast pot, wiper 05 ground 06 horiz sync or drive 07 + power (12 or 15 volts) 08 video 09 vert sync or drive 10 ground TTL levels or something like them on 6, 8, and 9. The connector's I've seen are either 10 pin .156 inch card edge or a 10 pin .1 molex header (single line). Here are some caveats: 1. If it's a high volume product, they may not have bothered following with this connector. 2. The video is very nonlinear, and inverted from the normal composite video. 0 volts = dark, TTL 1 = bright. 3. Sync must be provided, if you want interlace, you have to get the vertical timing just right. Even worse, some units don't have oscillators built in, and the inputs are drive signals with frequency and pulse width requirements. Get these wrong and the Horizontal Sweep circuit goes up in smoke. 4. You'll probably have to trap out the color subcarrier and sound. Most of these monitors are good for 8 to 12 Mhz. Markz@ssc.uucp