Zilog Z80180 - Manual (Page 31)

Z8018x
Family MPU User Manual
16
UM005003-0703
Figure 6. M1 Temporary Enable Timing
M1TE (M1 Temporary Enable): This bit controls the temporary assertion
of the M1 signal. It is always read back as a 1 and is set to 1 during
RESET. This function is used to arm the internal interrupt structure of the
Z80PIO. When a control word is written to the Z80PIO to enable
interrupts, no enable actually takes place until the PIO sees an active M1
signal. When M1TE is
1
, there is no change in the operation of the M1
signal and M1E controls its function. When M1TE is
0
, the M1 output is
asserted during the next Op Code fetch cycle regardless of the state
programmed into the M1E bit. This situation is only momentary (one
time) and the user need not reprogram a
1
to disable the function (See
Figure 7).
IOC: This bit controls the timing of the IORQ and RD signals. IOC is set
to
1
by RESET.
When IOC is
1
, the IORQ and RD signals function the same as the
HD64180.
Phi
WR
M1
Write into OMCR Op Code Fetch
T3 T2 T1 T1 T2 T3