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by greenbit
30 days ago
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The Commodore PET 4032 video system was generated by a 6545 (6845 equivalent) cathode ray tube controller, which generated the video buffer addresses and the HS and VS sync pulses. This was memory mapped and if one was not careful with POKE commands, you could effectively stop the CRT raster scan, leaving the beam parked at the center of the screen. This could burn the phosphors off that spot in a matter of minutes. Not exactly HCF, but a similar vibe. (The PET had its own monitor that, unlike common composite monitors of the era, apparently would not continue to scan when the sync went away) |
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I have also seen some monitors designed so badly, like the IBM MDA monitor mentioned at the link provided by userbinator, but all the TV sets that I have ever seen could only be synchronized to the desired scanning frequencies by the "sync" pulses, but they would oscillate freely in the absence of sync pulses.
The cost savings by not having relaxation oscillators or PLLs that would drive the raster scan in the absence of sync pulses, and which would limit the range of acceptable scan frequencies to safe values, have always been negligible, even by the time of the vacuum tube TV sets, and much more so by the time of computer monitors. The elimination of physical safety devices is not an acceptable way to reduce costs, especially when the savings are so small as in this case.