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M16C/26 Group
Rev.0.90 2003.12.28 page 7 of 28
Under development
Preliminary specification
Specifications in this manual are tentative and subject to change.
1.4 Precautions for DMAC
1.4.1 Write to DMAE Bit in DMiCON Register
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 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.
1.4 Precautions for DMAC