At 15:35 -0400 on 05/28/2009, Clark Kidd wrote about Punched Card
Combinations (WAS Book on Poughkeepsie):
As I remember, there were three "control" rows at the top of the
card (12, 11, 0) and then 9 "data" rows (1-9) under those. So each
possible column would contain up to 12 rows that could be punched:
Col1 Col2 ... Col80
12 12 12
11 11 11
0 0 0
1 1 1
2 2 2
3 3 3
4 4 4
5 5 5
6 6 6
7 7 7
8 8 8
9 9 9
For example, a column representing an "A" would have the first of
the control rows punched out (12), and the first of the data rows
(1) punched out. Some of the more exotic hex combinations required
quite a number of punches. For example, X'FF' was represented as
12-11-0-7-8-9. This is why a keypunch machine would be much louder
when you were duplicating an object dec
Actually as your X'FF' example shows, 8 and 9 were ALSO Control
Rows/Zones (ie: Punches could occur in any combination) and 1-7 were
data rows (one punch maximum in that Zone was allowed). Thus each
character was composed of one of 32 combinations of 12-1-0-8-9
punches and one or no punch in rows 1-7. The actual mappings between
Internal EBCDIC and Card Image EBCDIC were not always straight
forward.
I once had to design a program to read normal EBCDIC as Column Binary
(the card had mixed Column Binary and normal EBCDIC columns and there
was a need to convert the EBCDIC columns from their punches back into
real internal EBCDIC). It involved mapping the 12-11-0-8-9 punches as
the first 5 bits of a byte and coding the existence of a 1-7 punch as
the binary value in the low 3 bits. This card-image-binary was then
run though a TR table to convert it into the real internal EBCDIC.
That top and bottom 6 rows started in different bytes (interleaved)
so a TR to separate them into 2 contiguous blocks was first needed
before doing separate TRs to convert the punches into the bits which
was then followed by an OC to create the actual Card Image format.
There was also a Sanity Check pass that used TR tables to map the 1-7
punches as the low 7 bits of the byte followed by a TRT (in lieu of
the final conversion TR) to spot if there was more than one punch in
the 1-7 zone. The coding was simple. It was creating the Card Image
to Internal mapping TR Table that was fun.
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