Zilog Z86193 - Manual (Page 108)

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
Figure 97 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