In article , Richard Griffin
writes
"-Coded Octal" because each digit of the octal number is encoded
separately rather than treating the whole three-digit number as one unit.

In octal it's the same thing.

Sure. I should re-word the article to make it apparent that a hole for
"plat 3 to SB" doesn't actually clear the signal directly, merely
attempts to pull the relevant lever in the IMR when the electrical
interlocking allows. Is that correct? (Though AIUI, only some of the
Northern Line's ElectroPneumatic IMRs are still in use, others being
solid state replacements -- is this true?)

According to the book I'm looking at right now, the programme machine,
train describer logic, or the control panel push buttons all set a route
relay. The relay might work several signals according to track circuit
occupation; the relevant circuit powers the pneumatics for the IMR.

All the IMR-drive circuits also repeat the mechanical interlocking in
the electrical (that is, if levers 1 and 2 lock each other normal, the
2R circuit will go through a relay driven off 1 being normal and vice
versa). This means that the mechanical interlocking will not be stressed
by the pneumatic drives.

The programme machine roll is shown as 30 data tracks in two sets of 15,
with two control tracks, one punched in every row and one punched only
at the end of the row, between the sets. In the diagram, the left hand
set has 7 tracks used - 4 for the local train describer and 3 for three
possible routes. The right had set is:
- punched for first and last rows
- unused
- 4 tracks for train describer code to be transmitted on
- unused
- 8 tracks for train number, with the 200 bit on the left and the 1 bit
at the edge of the roll.

Other machines either have an interval field (5 holes, for 8,4,2,1, and
0.5 minutes) indicating how long to wait before moving the roll, or a
time code (11 holes, 8h,4h,2h,1h,32m,16m,8m,4m,2m,1m, and 0.5m)
indicating when to act on the remainder of the code.

A photo of a roll, however, doesn't agree with either. On the left side,
the first 7 bits are the destination code in some manner; matching with
the text typed on the roll, it says:
1000010 Morden Golders Grn. via B.
1111100 Morden High Barnet via C.X.
0011001 Kennington Edgware via C.X.
On the right hand side:
- tracks 1 and 2 alternate
- track 5 is punched for the Kennington trains and one other
- tracks 10 to 13 are punched with values that don't correlate with
either the train numbers (which include 9s) or the times. In sequence,
the codes are 7,6,4,3,2,11,10,9,13,1,5,15,14,12,8,7,6,4,3,2

--
Clive D.W. Feather, writing for himself | Home:
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