"Clive D. W. Feather" wrote in message
...
In article , Peter Corser
writes
As an aside you may be aware that the train running numbers (set numbers)
shown in the time table were the direct digital equivalent of a hex
number -
477 digital was stored as 477 hex and 477 was the highest number normally
used (there was also nothing between x78 and x99) which also saved bits
(ot
sequence machine fingers).

Actually, I think you'll find that numbers on programme machine controlled
lines only went up to 377 - there were 8 bits for train number.

The PM data I've seen wasn't organised by 8-bit byte, but simply had a
number of bits for each field. I thought that there were 6 minute bits, 5
hour bits, and a half-minute bit, but I could be misremembering here.

--
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Clive

You are right on the 4xx series numbers - some lines did have them for empty
trains, etc. but not on PM controlled lines.

The train numbers were octal (what's the correct term fo 2 bits giving
0-3?), but displayed as decimal using the same numerals, so 377 would be 8
bits overall.

It was 2 second time I was thinking about with the byte format. Your bit
numbering for the half minute time held on the machine seems familiar. I
think my brain is definitely getting addled - it's a long time since I
actuall did PM design (original Heathrow Extension), computer control system
with PM monitoring (Cobourg Street), LUL style computer control (Met,
Jubilee & Bakerloo) and Central Line. I think things have got a little
confused and blended with time!

Even when LUL had moved to computer control there was a tendency to to
define data structures using bit masks on the data - the GEC (later GPT)
4xxx series central control computers had their own data laid out like this.
I remember that the date information internally within the machine was based
on 0 in 1972 (I think Jan 1st) and included a year field which counted up -
this was a 6 bit field. We all thought that 5 bits would probably have been
enough!

Peter
--
Peter & Elizabeth Corser
Leighton Buzzard, UK




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