ZiLOG Z8 User Manual

Z8 Microcontrollers
ZiLOG Interrupts
UM001601-0803 7-5
7.4 INTERRUPT INITIALIZATION
After reset, all interrupts are disabled and must be initialized be-
fore vectored or polled interrupt processing can begin. The Inter-
rupt Priority Register (IPR), Interrupt Mask Register (IMR), and
Interrupt Request Register (IRQ) must be initialized, in that or
-
der, to start the interrupt process.
7.4.1 Interrupt Priority Register (IPR) Initializa-
tion
IPR (Figure 7-7) is a write-only register that sets priorities for the
vectored interrupts in order to resolve simultaneous interrupt re
-
quests. (There are 48 sequence possibilities for interrupts.) The
six interrupt levels IRQ0-IRQ5 are divided into three groups of
two interrupt requests each. One group contains IRQ3 and IRQ5.
The second group contains IRQ0 and IRQ2, while the third
group contains IRQ1 and IRQ4.
Priorities can be set both within and between groups as shown in
Tables 7-2 and 7-3. Bits 1, 2, and 5 define the priority of the in
-
dividual members within the three groups. Bits 0, 3, and 4 are en-
coded to define six priority orders between the three groups. Bits
6 and 7 are reserved.
Figure 7-7. Interrupt Priority Register
D7 D6 D5 D4 D3 D2 D1 D0
(Write-Only)
Interrupt Priority Register (IPR)
Register F9H
Interrupt Group Priority
Bits Priority
000 Reserved
001 C > A > B
010 A > B > C
011 A > C > B
100 B > C > A
101 C > B > A
110 B > A > C
111 Reserved
0 = IRQ1 > IRQ4
1 = IRQ4 > IRQ1
Group C (IRQ1 and IRQ4 Priority)
Reserved (Must be 0)
0 = IRQ2 > IRQ0
1 = IRQ0 > IRQ2
Group B (IRQ0 and IRQ2 Priority)
0 = IRQ5 > IRQ3
1 = IRQ3 > IRQ5
Group A (IRQ3 and IRQ5 Priority)
Tab le 7-2. Interrupt Priority
Priority
Group Bit Val ue Highest Lowest
C Bit 1 0 IRQ1 IRQ4
1 IRQ4 IRQ1
B Bit 2 0 IRQ2 IRQ0
1 IRQ0 IRQ2
A Bit 5 0 IRQ5 IRQ3
1 IRQ3 IRQ5
Tab le 7-3. 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

ZiLOG Z8 Specifications

General

Brand	ZiLOG
Model	Z8
Category	Desktop
Language	English