Zilog Z80180 - Manual (Page 298)

Z8018x
Family MPU User Manual
282
UM005003-0703
REQUEST PRIORITY
The Z80180 features three types of requests.
.
Type 1, Type 2, and Type 3 requests priority as follows.
•
Highest priority Type 1 > Type 2 > Type 3 lowest priority
•
Each request priority in Type 2 is shown as follows. highest priority
Bus Req.
> Refresh Req. > DMA Request lowest priority
Internal
I/O
Interrupt ­ ­ ­ ­ ­ ­ ­ Not
acceptable
NMI ­ ­ ­ Not acceptable
Interrupt
acknowledge
cycle precedes.
NMI is accepted
after executing Acceptable
DMA cycle
stops Acceptable
Return from
SYSTEM
STOP mode
to normal
operation
Note: * Not acceptable when DMA Request is in level-sense.
­: Same as above.
MC: Machine Cycle
Table 54. The Z80180 Types of Requests
Type 1 Accepted in specified state WAIT
Type 2 Accepted in each machine cycle Refresh Request, DMA
Request, and Bus Request.
Type 3 Accepted in each instruction Interrupt Request
Table 53. Request Acceptances in Each Operating Mode
Current
Status
Request
Normal
Operation
(CPU mode
and IOSTOP
Mode)
WAIT State
Refresh
Cycle
Interrupt
Acknowledge
Cycle
DMA Cycle
BUS
RELEASE
Mode
SLEEP
Mode
SYSTEM
STOP
Mode