Which paper tape hole is bit 1?
pkoning at equallogic.com
Fri Nov 18 10:49:43 CST 2005
>>>>> "Charles" == Charles <charlesmorris at direcway.com> writes:
Charles> Today I was hooking up my homebrewed driver board to the
Charles> M-series connector on the back of my Tally 420PR tape punch
Charles> (interfaces to my 8/A and . Fortunately, before I inserted
Charles> the eight data pins into the connector body it occurred to
Charles> me that Tally and DEC might not interpret the holes in the
Charles> same order. And indeed they don't!
Charles> The paper tape has five holes on one side of the sprocket
Charles> hole and three on the other. Typical DEC terminology is Bit
Charles> 1 = MSB and Bit 8 = LSB. Is that in fact how DEC labeled it?
Charles> Is the MSB on the outside of the 5-hole side or the 3-hole
Charles> side? Which hole on the tape is which?
DEC PDP-11 era terminology is bit 0 is LSB, bit 15 is MSB. The PDP-10
numbering is the reverse (bit 0 MSB). The only one I can think of
that labeled the MSB bit 1 is IBM...
Anyway, in the usage I have seen, the paper tape rows are numbered
sequentially with the LSB at the outside edge of the 3-row side.
Certainly that's how it shows up in DEC PDP11 papertape interfaces (so
the outside edge 3-row hole translates to the LSB, bit 0, in the data
once it shows up in the CSRs or in memory).
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