This might be slightly off topic but it does involve operation on a real 1620.
I have the coding for a transition program IBM wrote to help 1620 users move to 360/370 computers. I have a good portion of the code working but I've run into a snag testing out the Disk Utility Program. A sequence of instructions reads sector 04800 to core 00000-00099, the character at 00000 being a Record Mark. Ultimately the RM is moved to the Q11 position of of a TD instruction. The 1620 simulator fails trying to convert the Q address to binary since RM with a bit pattern of 1010 is not a valid decimal character. Since this sequence seems to work on real hardware, my question is: Is the RM and possibly Group Mark valid in a P or Q address and if so, what would be the value in the address? Could the RM be a 0 and the GM (1111) be a 5 using modulo 10. Any info would be appreciated.
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