IBM 5170 Technical Reference page 75

Low and High Memory Expansion Bytes (Hex 17 and 18)
Bit 7-Bit 0 Address hex 17-Low-byte expansion size
Bit 7-Bit 0 Address hex 18-High-byte expansion size
Valid Sizes:
0200H 512Kb I/O adapter
0400H 1024Kb
I/O
adapter (2 adapters)
600H 1536Kb I/O adapter (3 adapters)
to
3COOH 15360Kb
I/O
adapter (15Mb
maximum)
Hex addresses 19 through 2D are reserved .
.
~
Checksum (Hex 2E and 2F)
Address hex 2E High byte of checksum
Address hex 2F Low byte of checksum
Note: Checksum is on addresses hex 10-20.
Low and High Expansion Memory Bytes (Hex 30 and 31)
Bit 7-Bit 0 Address hex 30-Low-byte expansion size
Bit 7-Bit 0
Address hex 31-High-byte expansion size
Valid Sizes:
0200H 512Kb
I/O
adapter
0400H 1024Kb I/O adapter
System
Board 1-53