• Selecting condition codes for sequencer control. The first bit of field 1 indicates
whether the condition flag is to be set to 1 or 0, and the remaining 4 bits
indicate which flag is to be set.
• Sending an I/O request to the PC/AT.
• Enabling local data memory read/write operations.
• Determining the unit driving the system Y bus. One of the four devices attached
to the bus (Figure 16.17) is selected.