hase@netmbx.UUCP (Hartmut Semken) (05/14/88)
I think this is interesting not only to Michael Kieras, who asked me about "gelocking" the ST to an external signal. Please hit "n" if you do not know the right side of the soldering iron... >Hartmut Semken, Just call me hase, like everyone does.. > I read with extreme interest your letter on using the Hsync and Vsync >lines on the ST as a genlock input. But, since I really know nothing about the subject, I am left with many questions. I'll try to help You; does nobody else know about this? > First, I am guessing that Hsync and Vsynch apply to the RGB lines. No. They are just the synchrinisation lines for the ST video output; a pulse on HSync tells the Monitor (RGB or monochrome) to start a new scan line, VSync tells it to start a new screen. The frequency of 35 kHz on the HSync line (in monochrome video mode/high resolution) can be hazardous to color monitors (they exspect 15 kHz on this line) so be careful (a friend of mine killed his green monitor this way..) ! On the RGB lines the ST transmits the brightnes of the current pixel in its red, green and blue components. After pulsing HSync the ST starts to transmit a new line of 620 or 340 pixels. These are the basics; ask your local TV-freak for details (ok?). When operating "normal" the ST is source of the sychronisation signals: the GLUE/Shifter chips decide when to start a new line/picture and tell the monitor so (via H/V-Sync). When programmed for external synchronisation, the Shifter (shifting out the pixels serially after HSync, hence the name) takes the sync lines as inputs and synchronizes his shifting (and thereforethe ST picture) to the external signal. Now all you need are 2 VCRs with EURO AV (also called SCART) connector or any other [R+G+B+HSync+VSync+ground] input/output, a soldering iron, some wires, ST monitor plugs (about $3 around here in Germany) and a weekend: connect the VCRs and let one play (so it becomes SOURCE of a video (and synchronisation) signal) and the other one record (so it will synchronize on the input signals, you can use a monitor with RGB inputs here). If you now connect the RGB and Sync lines of the ST to the RGB and Sync lines of the VCR/Monitor *and* set the ST for external sync (how? hmm, its somewhere in the Abacus book "ST Internals" of Brueckmann/Englisch/Gerits, I think) and (voila!) the pictures are simply added (the brightness values for each pixel are added). To protect the ST you can do the connection over one-Microfarad-capacitators (almost never necassary but cheap and secure). That is all. This "genlock" cannot do bluebox tricks, of course. It is just possible to add the two pictures by synchronizing the ST to an external video source (like a camera to put in titles or the like). A bluebox genlock is a lot more difficult to make (and too much for my little knowledge..) and more expensive... Something wrong about this? I don't think so; I tried it out: We connected two STs to the same monitor, and programmed one for external sync. They both ran NeoChrome with the same picture but slightly different palettes. Looks great (and makes Amiga-Freaks run for shelter..:-). Still something wrong? I'm not perfect... Correct me! hase -- Hartmut Semken, Lupsteiner Weg 67, 1000 Berlin 37 hase@netmbx.UUCP I think, you may be right in what I think you're thinking. (Douglas Adams)
cmcmanis%pepper@Sun.COM (Chuck McManis) (05/17/88)
In article <1832@netmbx.UUCP> hase@netmbx.UUCP (Hartmut Semken) writes: > ...the pictures are >simply added (the brightness values for each pixel are added).... This is not as useful as one might hope. If you put a Grey title on the screen then you will be able to see 'through' it because the background is changing. It would be useful if the source VCR just played a black screen so that you could record the Atari's output on the VCR. >They both ran NeoChrome with the same picture but slightly different >palettes. Looks great (and makes Amiga-Freaks run for shelter..:-). Last time I checked one Amiga was a whole lot cheaper than two ST's and took up less desk space too :-) --Chuck McManis uucp: {anywhere}!sun!cmcmanis BIX: cmcmanis ARPAnet: cmcmanis@sun.com These opinions are my own and no one elses, but you knew that didn't you.