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Rev.1.02 Jul 01, 2005 page 286 of 314
REJ09B0126-0102
M16C/6N Group (M16C/6NL, M16C/6NN) 22. Usage Precaution
Under development
This document is under development and its contents are subject to change.
22.8 DMAC
22.8.1 Write to DMAE Bit in DMiCON Register (i = 0, 1)
When both of the conditions below are met, follow the steps below.
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.
Step 1: Write “1” to the DMAE bit and DMAS bit in the DMiCON register simultaneously
(1)
.
Step 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.