H8SSLASH2225 datasheet(337/1071 Pages) RENESAS

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Section 8 DMA Controller (DMAC)

Rev. 5.00 Aug 08, 2006 page 251 of 982

REJ09B0054-0500

8.5.7

Block Transfer Mode

In block transfer mode, data transfer is performed with channels A and B used in combination.

Block transfer mode can be specified by setting the FAE bit in DMABCRH and the BLKE bit in

DMACRA to 1. In block transfer mode, a data transfer of the specified block size is carried out in

response to a single transfer request, and this is executed for the number of times specified in

ETCRB. The transfer source is specified by MARA, and the transfer destination by MARB. Either

the transfer source or the transfer destination can be selected as a block area (an area composed of

a number of bytes or words). Table 8.10 summarizes register functions in block transfer mode.

Table 8.10 Register Functions in Block Transfer Mode

Function

Initial Setting

Operation

MARA

Source address

Start address of

transfer source

Incremented/decremented

every transfer, or fixed

MARB

Destination

address register

Start address of

transfer destination

Incremented/decremented

every transfer, or fixed

ETCRAH

Holds block

size

Block size

Fixed

ETCRAL

Block size

counter

Block size

Decremented every

transfer; ETCRH value

copied when count

reaches H'00

ETCRB

Block transfer

counter

Number of block

transfers

Decremented every block

transfer; transfer ends

when count reaches

H'0000

MARA and MARB specify the start addresses of the transfer source and transfer destination,

respectively, as 24 bits. MAR can be incremented or decremented by 1 or 2 each time a byte or

word is transferred, or can be fixed. Incrementing, decrementing, or holding a fixed value can be

set separately for MARA and MARB. Whether a block is to be designated for MARA or for

MARB is specified by the BLKDIR bit in DMACRA.

To specify the number of transfers, if M is the size of one block (where M = 1 to 256) and N

transfers are to be performed (where N = 1 to 65,536), M is set in both ETCRAH and ETCRAL,

and N in ETCRB.

Figure 8.14 illustrates operation in block transfer mode when MARB is designated as a block area.

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