Sharp MZ-80B Owner's Manual page 112

103
Table 4.4-1 lists how each flag bit is affected by various CPU instructions. In this table a
'e'
indicates that the
instruction does not change the flag, an 'X' means that the flag goes to an indeterminate state, a '0' means that it is
reset, a 'I' means that it is set and the symbol
't'
indicates that it is set or reset according to the previous discussion.
Note that any instruction not appearing in this table does not affect any of the flags.
Table 4.4-1 includes a few special cases that must be described for clarity. Notice that the block search instruction
sets the Z flag if the last compare operation indicated a match between the source and the accumulator data. Also, the
parity flag is set if the byte counter (register pair BC) is not equal to zero. This same use of the parity flag is made with
the block move instructions. Another special case is during block input or output instructions, here the Z flag is used to
indicate the state of register B which is used as a byte counter. Notice that when the I/0 block transfer is complete, the
zero flag will be reset to a zero (i.e. B
=
0) while in the case of a block move command the parity flag is reset when the
operation is complete. A final case is when the refresh or 1 register is loaded into the accumulator , the interrupt enable
flip flop is loaded into the parity flag so that the complete state of the CPU can be saved at any time.