Repeat Mode - Renesas H8S Series Hardware Manual

7.5.4

Repeat Mode

Repeat mode can be specified by setting the RPE bit in DMACR to 1, and clearing the DTIE bit to 0. In repeat mode,
MAR is updated after each byte or word transfer in response to a single transfer request, and this is executed the number
of times specified in ETCR. On completion of the specified number of transfers, MAR and ETCRL are automatically
restored to their original settings and operation continues.
One address is specified by MAR, and the other by IOAR. The transfer direction can be specified by the DTDIR bit in
DMACR.
Table 7-8 summarizes register functions in repeat mode.
Table 7-8 Register Functions in Repeat Mode
Register
23
23 15
H'FF
Legend:
MAR: Memory address register
IOAR: I/O address register
ETCR: Transfer count register
DTDIR:Data transfer direction bit
MAR specifies the start address of the transfer source or transfer destination as 24 bits. MAR is incremented or
decremented by 1 or 2 each time a byte or word is transferred.
IOAR specifies the lower 16 bits of the other address. The 8 bits above IOAR have a value of H'FF.
The number of transfers is specified as 8 bits by ETCRH and ETCRL. The maximum number of transfers, when H'00 is
set in both ETCRH and ETCRL, is 256.
In repeat mode, ETCRL functions as the transfer counter, and ETCRH is used to hold the number of transfers. ETCRL is
decremented by 1 each time a transfer is executed, and when its value reaches H'00, it is loaded with the value in ETCRH.
At the same time, the value set in MAR is restored in accordance with the values of the DTSZ and DTID bits in DMACR.
The MAR restoration operation is as shown below.
MAR = MAR – (–1)
DTDIR = 0 DTDIR = 1 Initial Setting
0
Source
address
MAR
register
0 Destination
address
IOAR
register
7 0
Holds number of
transfers
ETCRH
Transfer counter
7 0
ETCRL
DTID DTSZ
· 2 · ETCRH
Function
Destination Start address of
address transfer destination
register or transfer source
Source Start address of
address transfer source or
register transfer destination
Number of transfers
Number of transfers
Operation
Incremented/
decremented every
transfer. Initial
setting is restored
when value reaches
H'0000
Fixed
Fixed
Decremented every
transfer. Loaded with
ETCRH value when
count reaches H'00
Rev.6.00 Oct.28.2004 page 201 of 1016
REJ09B0138-0600H