Discussion:
Old IBM protocol IBM 1006
(too old to reply)
Anne & Lynn Wheeler
2006-07-12 00:41:15 UTC
Permalink
http://listserv.uark.edu/scripts/wa.exe?A2=ind0509&L=ibmvm&P=8109
note in the above referenced archive ... it mentions transmission as
reverse inverted
• ALC is transmitted "reverse inverted". For example, capital A is
0x31, but it's transmitted as 0x73. This makes it a major PITA to
read > off the wire.

my off-repeated story of doing our own mainframe terminal controller
at the univ.
http://www.garlic.com/~lynn/subtopic.html#360pcm

and somebody writing an article blaiming four of us for the mainframe
pcm controller business.

the ibm mainframe channel interface had been reverse engineered and a
channel interface controller card built for an interdata/3

the second or third bug we encountered was passing ascii from the
interdata/3 (programmed to emulate 2702 over the channel interface to
the mainframe) ... showed data was coming in all garbage. it took some
time to realize that the linescanner on the interdata/3 was taking the
leading bit off the line and storing it it in the high order bit
position of the byte ... while the linescanner in the 2702 was taking
the leading bit off the line and storing it in the low order bit
position of the byte.

as a result "ascii" arriving in the mainframe memory from a 2702
(linescanner) was "bit-reversed" ... and the ibm translate tables were
taking that into account.
Tim Shoppa
2006-07-12 13:49:19 UTC
Permalink
Post by Anne & Lynn Wheeler
as a result "ascii" arriving in the mainframe memory from a 2702
(linescanner) was "bit-reversed" ... and the ibm translate tables were
taking that into account.
Vaguely related: when I go over old DECUS submissions (say late 60's
and very early 70's) I often find that the files are exactly backwards:
last character comes first, first character comes last. My best (and so
far only) guess is that at some point they were transferred via paper
tape and the reversal occured then.

I actually have some primitive tools to scan ASCII and a couple common
DEC binary paper tape formats and look for this problem.

Tim.
j***@aol.com
2006-07-14 10:57:08 UTC
Permalink
Post by Tim Shoppa
Post by Anne & Lynn Wheeler
as a result "ascii" arriving in the mainframe memory from a 2702
(linescanner) was "bit-reversed" ... and the ibm translate tables were
taking that into account.
Vaguely related: when I go over old DECUS submissions (say late 60's
last character comes first, first character comes last. My best (and so
far only) guess is that at some point they were transferred via paper
tape and the reversal occured then.
Yup. It was very easy to do.
Post by Tim Shoppa
I actually have some primitive tools to scan ASCII and a couple common
DEC binary paper tape formats and look for this problem.
ISTR one Tape Prep job where the gal had reversed the binaries. If
the label was on the wrong end there isn't anything to prevent
reversal.

/BAH

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