At 07:10 -0400 on 10/18/2005, John P Baker wrote about Re: MVCIN instruction:
The 2540 was both a card reader and a card punch. There was a 2520 which was a card reader.
And a 2501 which was an Unbuffered Card Reader (unlike the others) where the card's data was transmitted as it passed the read station. I had some fun with a 2501 when a shop I was in replaced a 2540 with one and then found out that there was a set of programs that needed to read cards punched with both Column Binary and EBCDIC Data Columns at the same time. With the 2540, the programs would issue a Read Column Binary/No-Stacker-Select to get the 160 Column Binary Bytes followed by a Read EBCDIC/Stacker-Select/Data-Check-Off. Since you only got on crack at the card with the 2501, they had to be read as Column Binary and then have the EBCDIC columns converted from the internal version of Card Image to the real internal EBCDIC mappings. This was done with a sequence of TRs followed by a OC (to overlay rows 12-3 over rows 4-9) and a final TR to do the actual conversion from the Card Punch Image mapping to Internal mapping. The hardest part was creating the mapping TR table for that last TR (the other TR Tables were mechanical and a simple pattern of progressions).
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