Z8
®
CPU
User Manual
UM001604-0108
Interrupts
101
Interrupt Mask Register Initialization
The Interrupt Mask Register individually or globally enables or disables the six interrupt
requests (see
on page 102). When bit 0 to bit 5 are set to 1, the corresponding
interrupt requests are enabled. Bit 7 is the master enable and must be set before any of the
individual interrupt requests can be recognized. Resetting bit 7 globally disables all of the
interrupt requests. Bit 7 is set and reset by the EI and DI instructions. It is automatically
reset during an interrupt service routine and set following the execution of an Interrupt
Return (IRET) instruction.
Bit 7 must be reset by the DI instruction before the contents of the Interrupt Mask Register
or the Interrupt Priority Register are changed except:
•
Immediately after a hardware reset
•
Immediately after executing an interrupt service routine and before IMR bit 7 has
been set by any instruction
B
Bit 2
0
IRQ2
IRQ0
1
IRQ0
IRQ2
A
Bit 5
0
IRQ5
IRQ3
1
IRQ3
IRQ5
Table 20. Interrupt Group Priority
Bit Pattern
Group Priority
Bit 4
Bit 3
Bit 0
High
Medium
Low
0
0
0
Not Used
0
0
1
C
A
B
0
1
0
A
B
C
0
1
1
A
C
B
1
0
0
B
C
A
1
0
1
C
B
A
1
1
0
B
A
C
1
1
1
Not Used
Table 19. Interrupt Priority (Continued)
Group
Bit
Value
Priority
Highest
Lowest