M16C29 Datasheet, PDF (453/499 Pages) Renesas Technology Corp – RENESAS MCU M16C FAMILY / M16C/Tiny SERIES

M16C/29 Group
22. Usage Notes
22.5 DMAC
22.5.1 Write to DMAE Bit in DMiCON Register
When both of the conditions below are met, follow the steps below.
(a) Conditions
• The DMAE bit is set to 1 again while it remains set (DMAi is in an active state).
• A DMA request may occur simultaneously when the DMAE bit is being written.
(b) Procedure
(1) Write 1 to the DMAE bit and DMAS bit in DMiCON register simultaneously⁽¹⁾.
(2) Make sure that the DMAi is in an initial state⁽²⁾ in a program.
If the DMAi is not in an initial state, the above steps should be repeated.
NOTES:
1. The DMAS bit remains unchanged even if 1 is written. However, if 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, 1 should be written to
the DMAS bit in order to maintain a DMA request which is generated during execution.
2. Read the TCRi register to verify whether the DMAi is in an initial state. If the read value is equal to
a value which was written to the TCRi register before DMA transfer start, the DMAi is in an initial
state. (If a DMA request occurs after writing to the DMAE bit, the value written to the TCRi register
is 1.) If the read value is a value in the middle of transfer, the DMAi is not in an initial state.
Rev. 1.12 Mar.30, 2007 ^{page 429} of 458
REJ09B0101-0112