
DMA Registers
11-12
Table 11–1.DMA PRI Bits and CPU/DMA Arbitration Rules
DMA PRI
Bit Nos:
1 – 0
Description
0 0
DMA coprocessor access is lowerpriority than CPU access. If the DMA channel and
the CPU are requesting the same resource, then the CPU will proceed. These bits are
set this way at reset.
0 1
This setting selects rotating arbitration which sets priorities between the CPU and DMA
channel by alternating their accesses, but not exactly equally. Priority rotates between
CPU and DMA accesses when they conflict during consecutive instruction cycles
.
 The
first time the DMA channel and the CPU request the same resource, the CPU has prior-
ity. If, in the following instruction cycle, the DMA coprocessor and the CPU again re-
quest the same resource, the DMA has priority. Alternate access continues as long as
the CPU and DMA requests conflict in consecutive instruction cycles. When there is no
conflict in a previous instruction cycle, the CPU has priority.
1 0
Reserved.
1 1
DMA coprocessor access is higherpriority than CPU access. If the DMA channel and
the CPU are requesting the same resource, then the DMA will proceed.
Table 11–2.TRANSFER MODE (AUX TRANSFER MODE) Field Descriptions
TRANSFER
MODE
Bit Nos:
3 – 2 / (5 – 4)
Description
0 0
Transfers are not erminated by the transfer counter, and noautoinitialization is
performed. TCINT (transfer counter interrupt) and AUX TCINT can still be used to
cause an interrupt when the transfer counter makes a transition to zero. The DMA
channel continues to run. Note that the address continues to increment while the
transfer count rolls over to its maximum value of 0FFFF FFFFh.
0 1
Transfers are terminated by the transfer counter. No autoinitialization is performed. A
halt code of 10
2
 is placed in the START (or AUX START) field when transfers are
completed.
1 0
Autoinitialization is performed when the transfer counter goes to zero without waiting
for CPU intervention.
1 1
The DMA channel is autoinitialized when the CPU restarts the DMA coprocessor by
using the DMA register in the CPU. When the transfer counter goes to zero,
operation is halted until the CPU starts the DMA coprocessor by using the START
(AUX START) field in the DMA channel control register (bits 22–23 and 24–25,
Table 11–5). A halt code of 10
2
 is placed in the START (or AUX START) field by the
DMA coprocessor.