Introduction and RK05J Drive cabling

Noel Chiappa jnc at
Sat Jan 23 07:22:59 CST 2016

    > From: Guy Sotomayor

    > To that end, I've made new "paddle" board that take 2 60pin ribbon
    > cables.

Guy, this is fantastic news! I have previously speculated about doing this,
but it's still on the 'someday' list.

    > I'll let folks know how they turn out (ie do they actually work!).

They should. DEC made the same basic part, but using 3x40-pin cables: M9042
(half-length, knuckle-buster) and M9014 (full-length). Apparently the
characteristic impedance of N-pin flat cable is close enough to the BC11
cable that it works.

Speaking of M9014's, though, the board list describes them as "UNIBUS to 3
H854s", and also lists an M9015, described as "3 H854s to UNIBUS". Does
anyone know what the difference is between the two?

Unlike the QBUS, the UNIBUS shouldn't need two different kinds of board, since
the 'grant in' pin on one end of a UNIBUS cable is the same as the 'grant out'
pin on the other end (unlike the QBUS, where the pinout is designed to support
plugging in boards, so there are separate 'grant in' and 'grant out' pins). I
can't for the life of me think of anything about the UNIBUS that a straight
through-connect wouldn't handle - i.e. a pair of M9014's, on each end of the
cable set. Certainly, BC11 cables ends aren't marked 'in' and 'out'! ;-)

So does anyone know why the M9015 exists - what it different about it, etc,
etc? Or was someone at DEC just not thinking hard enough when they spec'd it?

    > The downside is that they were somewhat expensive

Heh, they'll still be cheaper than actual BC11's! :-)


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