1 Mar
2008
1 Mar
'08
8:51 p.m.
Tim Riker wrote:
I have 4 HP-12531 cards. Two are have tabs labeled "HS TERMINAL" and 2
have labels "BUF'R'D TTY REG".
Three of cards have 307.200 Khz crystals, and one of the non-HS boards
has a 225.280 Khz crystal.
I'll just add that that was the conclusion (= except for the crystal) I came to
when I was working on the 12531D, based on a correlation between a physical
12531D (HST) and info in the manual for the 12531C (BUF'D TTY).
If it helps any, there are usually two numbers (at least) on the HP PCBs, one
in foil and one in ink, the foil number specifies the foil pattern, the ink
number specifies the component population.
(I also looked back at the 12531B manual, and IIRC, concluded the C&D are
essentially the B with a crystal oscillator and 2 div-by-16 chips replacing the
RC oscillator. I believe the B would function as a D if provided with an
appropriate clock.)
From what I read in:
http://www.bitsavers.org/pdf/hp/21xx/interfaces/12531C.pdf
and on:
http://www.cs.ubc.ca/~hilpert/e/HP21xx/io12531BCD.html
the only difference I can see between the C and the D is the crystal.
Does anyone know of another difference? Ok, here's the big one. Anyone know where to get
another 307.200 Khz
crystal? :)
Rather than looking for another 307 crystal, you're supposed to acquire a TTY,
so you can use it at 110 baud with the 225 crystal. :)
(More seriously) If necessary, there is an EXT CLK input on the connector - one
could whip up a 1.8432 or 4.9152 MHz integrated crystal clock (common on
scrapper '80/'90s serial boards) with another 74xx divider chip and feed it in.