M16C6K9 Datasheet, PDF (245/292 Pages) Renesas Technology Corp – SINGLE-CHIP 16-BIT CMOS MICROCOMPUTER

M16C/6K9 Group
Usage precaution
DMAC
The write to DMAC bit of DMAiCON register (i= 0-1)
If (a) conditions are matched, follow (b) as wirte procedure.
(a) Conditions
Write "1" to DMAE bit again when DMAE bit is "1" (DMAi active status).
The possibility that the write to DMAE bit and DMA request occur at the same time.
.
(b) Write procedure
(1) Write "1" to both DMAE bit and DMAS bit at the same time (Note 1).
(2)Confirm with program that DMAi is at initial condition (Note 2).
Note 1: The DMAS will be "0" if writing "0" to it. However, there is no change if writing "1" to the bit. Hence,
if "1" is to be written to DMAE by writing DMAiCON register, setting the value of DMAS to "1", DMAS
will remain the same status before the writing.
If read modify write command is used to write to DMAE bit, setting the value of DMAS to "1", the
DMA request will be retained during the execution of the command.
Note 2: Comfirm it with TCRi register.
If the value read from TCRi register becomes the same with that, which was written to TCRi register
before the start of DMA transfer (the TCRi value will be 1 decremented after writing to DMAE bit), it
is at initial condition. Otherwise, DMA is still under transfer.
Rev.1.00 Jun 06, 2003 page 245 of 290