User's Manual

Rev.1.10 Jul 01, 2005 page 90 of 318

REJ09B0124-0110

M16C/6N Group (M16C/6NK, M16C/6NM) 11. DMAC

Under development

This document is under development and its contents are subject to change.

11.3 DMA Enable

When a data transfer starts after setting the DMAE bit in the DMiCON register (i = 0, 1) to “1” (enabled), the

DMAC operates as follows:

(1) Reload the forward address pointer with the SARi register value when the DSD bit in the DMiCON register

is “1” (forward) or the DARi register value when the DAD bit in the DMiCON register is “1” (forward).

(2) Reload the DMAi transfer counter with the DMAi transfer counter reload register value.

If the DMAE bit is set to “1” again while it remains set, the DMAC performs the above operation.

However, if a DMA request may occur simultaneously when the DMAE bit is being written, follow the steps

below.

Step 1: Write “1” to the DMAE bit and DMAS bit in the DMiCON register simultaneously.

Step 2: Make sure that the DMAi is in an initial state as described above (1) and (2) in a program.

If the DMAi is not in an initial state, the above steps should be repeated.

11.4 DMA Request

The DMAC can generate a DMA request as triggered by the cause of request that is selected with the DMS

and DSEL3 to DSEL0 bits in the DMiSL register (i = 0, 1) on either channel. Table 11.4 shows the timing at

which the DMAS bit changes state.

Whenever a DMA request is generated, the DMAS bit is set to “1” (DMA requested) regardless of whether

or not the DMAE bit is set. If the DMAE bit was set to “1” (enabled) when this occurred, the DMAS bit is set

to “0” (DMA not requested) immediately before a data transfer starts. This bit cannot be set to “1” in a

program (it can only be set to “0”).

The DMAS bit may be set to “1” when the DMS or the DSEL3 to DSEL0 bits change state. Therefore,

always be sure to set the DMAS bit to “0” after changing the DMS or the DSEL3 to DSEL0 bits.

Because if the DMAE bit is “1”, a data transfer starts immediately after a DMA request is generated, the

DMAS bit in almost all cases is “0” when read in a program. Read the DMAE bit to determine whether the

DMAC is enabled.

Table 11.4 Timing at Which DMAS bit Changes State

i = 0, 1

DMA Factor

DMAS Bit in DMiCON Register

Timing at which the bit is set to “1” Timing at which the bit is set to “0”

Software Trigger When the DSR bit in the DMiSL register • Immediately before a data transfer starts