M16C65 Datasheet, PDF (317/829 Pages) Renesas Technology Corp – RENESAS MCU M16C FAMILY / M16C/60

Under development
M16C/65 Group
Preliminary Specification
This is a preliminary specification and is subject to change.
16. DMAC
16.5 Notes on DMAC
16.5.1 Write to the DMAE Bit in the DMiCON Register (i = 0 to 3)
When both of following conditions are met, follow steps (1) and (2) below.
• Write a 1 (DMAi is in active state) to the DMAE bit when it is 1.
• A DMA request may occur simultaneously when the DMAE bit is being written.
Steps
(1) Write a 1 to the DMAE bit and DMAS bit in the DMiCON register simultaneously ⁽¹⁾.
(2) Make sure that the DMAi is in an initialized state ⁽²⁾ in a program.
If the DMAi is not in an initialized state, repeat these two steps.
Notes:
1. The DMAS bit remains unchanged even if a 1 is written. However, if a 0 is written to this bit, it is
set to 0 (DMA not requested). In order to prevent the DMAS bit from being modified to 0, 1
should be written to the DMAS bit when 1 is written to the DMAE bit. In this way, the state of the
DMAS bit immediately before being written can be maintained.
Similarly, when writing to the DMAE bit with a read-modify-write instruction, write a 1 to the
DMAS bit to maintain a DMA request which is generated during execution.
2. Read the TCRi register to verify whether the DMAi is in an initialized state.
If the read value is equal to a value that was written to the TCRi register before DMA transfer
start, the DMAi is in an initialized state. (When a DMA request occurs after writing to the DMAE
bit, the read value is a value written to the TCRi register minus one.) If the read value is a value
in the middle of a transfer, the DMAi is not in an initialized state.
16.5.2 Changing DMA Request Source
When the DMS bit or bits DSEL4 to DSEL0 in the DMiSL register are changed, the DMAS bit in the
DMiCON sometimes becomes 1 (DMA requested). Set the DMAS bit to 0 (DMA not requested) after
the DMS bit or bits DSEL4 to DSEL0 in the DMiSL register are changed.
REJ09B0484-0030 Rev.0.30 Sep 09, 2008
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