copy of old manual

I have a hobby project with an old CP/M-80 system where the monochrome monitor is showing its age as the image is flickering a lot. I was wondering if I could attach a modern monitor or tv-screen, but I am not sure what standard the signal is called today.

I found this page describing the monitor characteristics (as far as I can tell from https://datamuseum.dk/bits/30001066 an adapted version of a NEC JB-1201M(A)), which says

  • 50 Hz frame frequency.
  • 275 active scan lines
  • 33 vertical blanking intervals
  • 308 total scan lines
  • 15.4 kHz line frequency ~= 65 microsecond line period time

Is this just simply 240p (which my game capture device will be able to understand when I get a BNC-RCA adapter cable) or is it called something else?

1 Answer 1


It's not 240p because that's generally a term for 60 Hz non-interlaced signal. You have 275 active lines which is more that the 240 active lines, and even more than the total 262 lines for a 240p signal.

A 50Hz non-interlaced signal has typically 312 total lines at 15.625 kHz so this signal with 15.4 kHz and 308 lines should be approximately compatible with any TV system capable of displaying a 50 Hz 625-line monochrome signal. This includes monochrome TVs, PAL TVs and SECAM TVs.

So best name for this 50 Hz signal could be 288p as it is compatible with 576i.

  • Ah, PAL makes sense as this is an European system. 576i sounds like most tv's around here will be capable,. Thanks. Jul 2, 2021 at 11:23
  • 2
    @MartinMaly I deliberately did not mention PAL because it is only a color encoding method that can be used with any TV system, and the device outputs a monochrome signal and any TV which can show a 50 Hz 625-line signal can show it, including monochrome TVs, PAL TVs and SECAM TVs.
    – Justme
    Jul 2, 2021 at 12:50
  • @Justme Nevertheless, PAL is commonly understood as referring to a 625-line 50Hz frame format, particularly in contrast to NTSC.
    – Chromatix
    Jul 6, 2021 at 10:43

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