
Z8 Microcontrollers
Interrupts
ZiLOG
UM001600-Z8X0599
7-11
7.6.1 Vectored Interrupt Cycle Timing
The interrupt acknowledge cycle time is 24 internal clock
cycles and is shown in Figure 7-13. In addition, two internal
clock cycles are required for the synchronizing flip-flops.
The maximum interrupt recognition time is equal to the
number of clock cycles required for the longest executing
instruction present in the user program (assumes worst
case condition of interrupt sampling, Figure 7-6, just prior
to the interrupt occurrence). To calculate the worst case in-
terrupt latency (maximum time required from interrupt gen-
eration to fetch of the first instruction of the interrupt ser-
vice routine), sum these components:
Worst Case Interrupt Latency
≈
24 INT CLK (interrupt ac-
knowledge time) + # T
P
C of longest instruction present in
the user's application program + 2T
P
C (internal synchroni-
zation time).
Figure 7-13. Z8 Interrupt Acknowledge Timing
PC
For Stack External Only
PC+1
PC
PCL
SP-1
SP-2
PCH
SP-3 FLAGS
VECT
VECT+1
Even Vector Address
Odd Vector Address
Op Code (Discarded)
VECTH
VECTL
First Instruction Of Interrupt Service Routine
For Stack External Only
A0-A7 IN
Internal Clock
/AS
/DS
A0-A7 OUT
M3
M1
M2
M1
M2
Stack Push
Fetch
Vector High
Fetch
Vector Low
Stack Push
Stack Push
R/W