LSI 53C810A - Manual (Page 164)

6-24 Instruction Set of the I/O Processor
The Add operation is used to increment or decrement register values (or
memory values if used in conjunction with a Memory-to-Register Move
operation) for use as loop counters.
6.5.4 Move To/From SFBR Cycles
All operations are read-modify-writes. However, two registers are
involved, one of which is always the SFBR. The possible functions of this
instruction are:
•
Write one byte (value contained within the SCRIPTS instruction) into
any chip register.
•
Move to/from the SFBR from/to any other register.
•
Alter the value of a register with AND, OR, ADD, XOR, SHIFT LEFT,
or SHIFT RIGHT operators.
•
After moving values to the SFBR, the compare and jump, call, or
similar instructions may be used to check the value.
•
A Move-to-SFBR followed by a Move-from-SFBR is used to perform
a register-to-register move.