ZiLOG Z80-CPU Technical Manual page 46

Table 6.0-1 lists how each flag bit is affected by various
C~U
instructions. In this table a '.' indicates
that the instruction does not change the flag, an 'X' means that the flag goes to an indeterminate state, a '0'
m~ans that it is reset, a '1' means that
it
is set and the symbol
'~'
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 6.0-1 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 Be) 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/O block transfer is complete, the zero flag will be reset to a zero (i.e. B=O)
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 I register is loaded into the accumulator, the interrupt enable flip flopis loaded
into the parity flag so that the complete state of the CPU can be saved at any time.
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