Sharp MZ-80B - Page 127

120
Ml
D 0- 0 7 ----(~)------~GJI--------
--------- r--------------
lEI _________ j
lEO
FIGURE 6-0-2
RETURN FROM INTERRUPT CYCLE
HIGHEST PRIORITY PORT
+
PORT1A PORT1B PORT 2A PORT 28
HI
lEO
1_ PRIORITY INTERRUPT DAISY CHAIN BEFORE ANY INTERRUPT OCCURS_
+
UNDER SERVICE
LO
lEI
lEO
2. PORT 2A REQUESTS AN INTERRUPT AND IS ACKNOWLEDGED.
+
UNDER SERVICE
lEO
3. PORT 18 INTERRUPTS, SUSPENDS SERVICING OF PORT 2A.
+
SERVICE COMPLETE SERVICE RESUMED
HI HI
lEO
4. PORT 18 SERVICE ROUTINE COMPLETE, "RETI" ISSUED, PORT 2A SERVICE RESUMED.
+
lEO
5. SECOND "RETI" INSTRUCTION ISSUED ON COMPLETION OF PORT 2A SERVICE ROUTINE.
FIGURE 6.0-3
DAISY CHAIN INTERRUPT SERVICING