Programmable Option Select; Description; Section 2. Programmable Option Select - IBM Personal System/2 50 Technical Reference

Description
Programmable Option Select (POS) eliminates the need for switches
by replacing their function with programmable registers. This section
describes the POS information used on the Model 50 system board.
For additional POS information, refer to the Hardware Interface
Technical Reference.
Warning:
• IBM recommends that programmable options be set only through
the System Configuration utilities. Directly setting the POS
registers or CMOS RAM POS parameters can cause multiple
assignment of the same system resource, improper operation of
the feature, loss of data, or possible damage to the hardware.
• Application programs should not use the adapter identification
(10) unless absolutely necessary. Compatibility problems can
result.
• If an adapter and the system board are in setup mode at the same
time, bus contention will occur, no useful programming can take
place, and damage to the hardware can occur.
• After setup operations are complete, the Adapter Enable/Setup
register (hex 0096) should be set to hex 00, and the System Board
Enable/Setup register (hex 0094) should be set to hex FF.
• The channel reset bit (bit 7) in the Adapter Enable/Setup register
must be 0 to program the adapters.
• The system board does not support 16-bit I/O operations to 8-bit
POS registers. Using 16-bit I/O instructions on 8-bit POS
registers will cause erroneous data to be written to or read from
the registers. Only 8-bit transfers are supported for setup
operations.
Model 50 POS 2-3