19 Nov
2005
19 Nov
'05
4:22 a.m.
Err, that depends on the DEC machine. My PDP11 has bit
0 as the LSB and
bit 15 asn the MSB. The PDP8/e on my desk has bit 0 as the MSB and bit
11 as the LSB . I don't know of any DEC machine that has bit 1 as the MSB
Actually I was referring to the labels within the PC8E schematic
where the punch lines are labeled "HOLE1" through "HOLE8". I agree
that bits should start at 0, and usually do...
As it turns out Hole 8..1 corresponds on a PDP-8 to data bits
4..11 respectively (more significant to least significant). I was
surprised since I expected the hole numbers to increase directly
with the data bit number.
I also found in the archives a copy of the manual DEC-08-NGCC-D
(PDP-8 Family Paper Tape Systems User's Guide) and on page 26/155
(manual page Intro-13) there is a nice diagram of the 8-bit tape.
So in conclusion the relationships on a PDP-8 are as follows:
Holes: 87654x321
Significance: MSB.......LSB
Data bus bits: D4.......D11
The punch is now hooked up (correctly) via my homebrewed driver
card to the PC8E interface, and merrily spews chad all over the
floor at high speed! I can email an Eagle schematic/board layout
for the drive card if anyone wants...
Now looking for a Tally 420 chad bucket :)
-Charles