Path: utzoo!attcan!uunet!tut.cis.ohio-state.edu!ucbvax!hplabs!hpfcdc!hpfcdj!myers From: myers@hpfcdj.HP.COM (Bob Myers) Newsgroups: sci.electronics Subject: Re: sync signal generator Message-ID: <17660008@hpfcdj.HP.COM> Date: 8 Aug 89 18:16:22 GMT References: <89216.120136BHB3@PSUVM> Organization: Hewlett Packard -- Fort Collins, CO Lines: 40 >RS-170 is monochrome. Isn't the 3-wire RGB RS-170-like video spec RS-343? >I can't remember anymore. Nope. RS-170 IS monochrome, but the version of RS-170 which includes the NTSC color encoding scheme (with accompanying slight changes in timing) is RS-170A. RS-343 (now superseded by at least RS-343A) was intended as a high-resolution closed-circuit standard; RS-343A never really caught on as far as its recommended timing (it is an interlaced standard), but the signal level definitions are used by most high-resolution computer graphics displays today. The signal levels defined for these standards are (all into 75 ohms, and assuming the BLANK (not the BLACK) level as the reference: RS-170/170A: White is 1V POSITIVE from reference Sync tips 0.4V NEGATIVE from reference. (Overall 1.4V p-p signal) RS-343/343A: White is 0.714V POSITIVE from reference. Sync tips 0.286V NEGATIVE from reference. (1.0V p-p overall.) In RGB systems conforming to these standards, the sync is on the GREEN signal. The red and blue signals conform to the signal level standards w/o the sync, i.e., the red and blue in an RS-343-level system would be expected to have a max. swing of 0.714Vp-p. Sync may also be provided to the monitor via a separate input or inputs, which are usually TTL-compatible. Back to the original question - I don't quite understand the needs of your system. If the unit simply requires an external Vsync pulse to "sync up to" before it will produce video, then simply feed it the output of a pulse generator set to make 60 Hz with about a 2-3% duty cycle (sync pulse about 0.3 - 0.4 msec long, out of the 16.67 period). This will result in video which should be usable by any RS-170 monochrome display; no need to get the 59.94 Hz NTSC timing exactly, unless you're planning on syncing up to some external video. But in the latter case, you'd want to derive the Vsync signal from that external source anyway - and that's a whole 'nother can of worms! Bob Myers KC0EW HP Graphics Tech. Div.| Opinions expressed here are not Ft. Collins, Colorado | those of my employer or any other myers%hpfcla@hplabs.hp.com | sentient life-form on this planet.