[Simh] Non-numeric character in IBM 1620 P & Q addresses

[Michael Short]

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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