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M16C/29 Group
11.3 DMA Enable
When a data transfer starts after setting the DMAE bit in DMiCON register (i = 0, 1) to "1" (enabled), the
DMAC operates as follows:
(1) Reload the forward address pointer with the SARi register value when the DSD bit in DMiCON register
is "1" (forward) or the DARi register value when the DAD bit of DMiCON register is "1" (forward).
(2) Reload the DMAi transfer counter with the DMAi transfer counter reload register value.
If the DMAE bit is set to "1" again while it remains set, the DMAC performs the above operation. However,
if a DMA request may occur simultaneously when the DMAE bit is being written, follow the steps below.
Step 1: Write "1" to the DMAE bit and DMAS bit in DMiCON register simultaneously.
Step 2: Make sure that the DMAi is in an initial state as described above (1) and (2) in a program.
If the DMAi is not in an initial state, the above steps should be repeated.
11.4 DMA Request
The DMAC can generate a DMA request as triggered by the cause of request that is selected with the
DMS and DSEL3 to DSEL0 bits of DMiSL register (i = 0, 1) on either channel. Table 11.4.1 shows the
timing at which the DMAS bit changes state.
Whenever a DMA request is generated, the DMAS bit is set to "1" (DMA requested) regardless of whether
or not the DMAE bit is set. If the DMAE bit was set to "1" (enabled) when this occurred, the DMAS bit is
set to "0" (DMA not requested) immediately before a data transfer starts. This bit cannot be set to "1" in
a program (it can only be set to "0").
The DMAS bit may be set to "1" when the DMS or the DSEL3 to DSEL0 bits change state. Therefore,
always be sure to set the DMAS bit to "0" after changing the DMS or the DSEL3 to DSEL0 bits.
Because if the DMAE bit is "1", a data transfer starts immediately after a DMA request is generated, the
DMAS bit in almost all cases is "0" when read in a program. Read the DMAE bit to determine whether the
DMAC is enabled.
Table 11.4.1 Timing at Which the DMAS Bit Changes State
DMA factor
Software trigger
Peripheral function
Rev.1.00 Nov 01,2004
REJ09B0101-0100Z
DMAS bit of the DMiCON register
Timing at which the bit is set to "1"
When the DSR bit of DMiSL
register is set to "1"
When the interrupt control register
for the peripheral function that is
selected by the DSEL3 to DSEL0
and DMS bits of DMiSL register
has its IR bit set to "1"
page 91 of 402
Timing at which the bit is set to "0"
• Immediately before a data transfer starts
• When set by writing "0" in a program
11. DMAC
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