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The DECscope User's manual (EK-VT5X-OP-001, 4th printing, March 1977) states (page 19) that Reverse Line Feed is VT52/VT55 only:

Reverse Line Feed (VT52 only)

invoked by ESC I (033 111)

...

However, vt50h termcap/terminfo entries, dating back at least to 2BSD (1980), include reverse linefeed. (vt50 termcap/terminfo entries do not).

$ infocmp vt50h
#   Reconstructed via infocmp from file: /usr/share/terminfo/76/vt50h
vt50h|dec vt50h,
    cols#80, lines#12,
    bel=^G, clear=\EH\EJ, cr=^M, cub1=^H, cud1=^J, cuf1=\EC,
    cup=\EY%p1%' '%+%c%p2%' '%+%c, cuu1=\EA, ed=\EJ, el=\EK,
    ht=^I, ind=^J, ri=\EI,

Did the VT50h support reverse linefeed?

2

It seems that this is a mistake from the terminfo entry (it wouldn't be the first).

The only difference between the VT50 and VT50H is the keypad, not the command set, and another document from DEC: VT50 user's manual (issued in 1975), clearly indicates, consistently with the document you mentioned, that "ESC I" has no effect on the VT50 (see page 19).

There is no reason not to trust both these documents from DEC.

I personally have, on the other hand, more than one reason to distrust a terminfo entry.

3
  • Per the DECScope user manual, VT50H also supported cursor down (ESC B) and Direct cursor addressing (ESC Y or SO). – Kelvin Sherlock Mar 7 '18 at 3:10
  • @KelvinSherlock You are right, there are some differences in the command set between the VT50 and VT50H, that I wasn't aware of. Well, I am still convinced that if there is a mistake somewhere, it is much more likely to be in the terminfo than in the DECscope manual, but since I was using the hypothesis that both VT50 and VT50H have the same command set in my answer, and I am unable to find a specific manual for VT50H, I wonder what to do with my answer. Shall I delete it? – dim Mar 7 '18 at 8:54
  • It's a good answer (and following your link I did find the service notes which includes the vt50 microprogramming). Short of digging up the VT50H microprogramming or someone actually testing, it's probably the correct answer. – Kelvin Sherlock Mar 7 '18 at 15:57

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