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Section 13 Direct Memory Access Controller (DMAC)
Rev. 4.00 Sep. 14, 2005 Page 419 of 982
REJ09B0023-0400
If (PR1 and PR0) = (B'10) is specified, the channel priority is determined according to the settings
of the round-robin select bits. In this case, the channel priority is changed between channels
whose corresponding round-robin select bit is set to 1. If (PR1 and PR0) = (B'01) is specified, the
channel priority is specified as fixed mode 2 (CH0 > CH2 > CH3 > CH1). If (PR1 and PR0) =
(B'11) is specified, the channel priority is specified as the all-channel round-robin mode. If (PR1
and PR0) = (B'00) is specified, the channel priority is specified as fixed mode 1 (CH0 > CH1 >
CH2 > CH3). Note that the round-robin select bit values are ignored except when (PR1 and PR0)
= (B'10) is specified.
If the round-robin select bit or the priority mode bit is modified after a DMA transfer, the channel
priority is initialized to be changed. If fixed mode 2 is specified, the channel priority is specified
as CH0 > CH2 > CH3 > CH1. If fixed mode 1 is specified, the channel priority is specified as
CH0 > CH1 > CH2 > CH3. If a mode including round-robin mode is specified again, the transfer
end channel is reset.
Table 13.2 summarizes the relationship among the round-robin select bits, priority bits, channel
priority, and priority modes (mode 0 to mode 7). Each priority mode includes up to five kinds of
channel priority according to the transfer end channel.
For example, if the round-robin select bits are specified as (RC0 to RC3) = (B'1110) to select
mode 3 and if the transfer end channel is channel 1, the priority of the channel to accept the next
transfer request is specified as CH0 > CH1 > CH2 >CH3. When the channel on which the transfer
was just finished is CH3, CH3 is not intended for round-robin. Therefore the priority level is not
changed.