H8SXSLASH1663R datasheet(533/1504 Pages) RENESAS

533 / 1504 page

Section 11 EXDMA Controller (EXDMAC)

Rev. 2.00 Sep. 24, 2008 Page 501 of 1468

REJ09B0412-0200

When EDDAR is read during a transfer operation, a longword access must be used. During a

transfer operation, EDDAR may be updated without regard to accesses from the CPU, and the

correct values may not be read if the upper and lower words are read separately. Do not write to

EDDAR for a channel on which a transfer operation is in progress.

(3)

EXDMA Transfer Count Register (EDTCR)

When an EXDMA transfer is performed, the value in EDTCR is decremented by the number of

bytes transferred. When a byte is transferred, the value is decremented by 1; when a word is

transferred, the value is decremented by 2; when a longword is transferred, the value is

decremented by 4. However, when the EDTCR value is 0, transfers are not counted and the

EDTCR value does not change.

All of the bits of EDTCR may change, so when EDTCR is read by the CPU during EXDMA

transfer, a longword access must be used. During a transfer operation, EDTCR may be updated

without regard to accesses from the CPU, and the correct values may not be read if the upper and

lower words are read separately. Do not write to EDTCR for a channel on which a transfer

operation is in progress.

If there is conflict between an address update associated with EXDMA transfer and a write by the

CPU, the CPU write has priority.

In the event of conflict between an EDTCR update from 1, 2, or 4 to 0 and a write (of a nonzero

value) by the CPU, the CPU write value has priority as the EDTCR value, but transfer is

terminated.

(4)

EXDMA Block Size Register (EDBSR)

EDBSR is valid in block transfer or repeat transfer mode. EDBSR31 and EDBSR16 are used as

BKSZH and EDBSR15 and EDBSR0 for BKSZ. The 16 bits of BKSZH holds a block size and

repeat size and their values do not change. The 16 bits of BKSZ functions as a block size or repeat

size counter, the value of which is decremented by 1 when one data transfer is performed. When

the BKSZ value is determined as 0 during EXDMA transfer, the EXDMAC does not store 0 in

BKSZ and stores the BKSZH value.

The upper 16 bits of EDBSR is never updated, allowing a word-size access.

Do not write to EDBSR for a channel on which a transfer operation is in progress.

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