Zilog Z80180 - Manual (Page 129)

Z8018x
Family MPU User Manual
114
UM005003-0703
DMAC Internal Interrupts
Figure 50 illustrates the internal DMA interrupt request generation circuit.
Figure 50. DMA Interrupt Request Generation
DE0 and DE1 are automatically cleared to
0
by the Z8X180 at the
completion (byte count is
0
) of a DMA operation for channel 0 and
channel 1, respectively. They remain
0
until a
1
is written. Because DE0:
and DE1 use level sense, an interrupt occurs if the CPU IEF1 flag is set to
1
. Therefore, the DMA termination interrupt service routine disables
further DMA interrupts (by programming the channel DIE bit is
0
) before
enabling CPU interrupts (for example, IEF1 is set to
1
). After reloading
the DMAC address and count registers, the DIE bit can be set to
1
to
reenable the channel interrupt, and at the same time DMA can resume by
programming the channel DE bit =
1
.
DMAC and NMI
NMI, unlike all other interrupts, automatically disables DMAC operation
by clearing the DME bit of DSTAT. Thus, the NMI interrupt service
routine responds to time-critical events without delay due to DMAC bus
usage. Also, NMI can be effectively used as an external DMA abort input,
recognizing that both channels are suspended by the clearing of DME.
DE1
DIE1
DE0
DIE0
IEF1
DMA ch1 Interrupt
Request
DMA ch0 Interrupt
Request