Usage Notes - Hitachi H8S/2338 Series Hardware Manual

5.7

Usage Notes

DMAC Register Access during Operation: Except for forced termination, the operating
(including transfer waiting state) channel setting should not be changed. The operating channel
setting should only be changed when transfer is disabled.
Also, MAC registers should not be written to in a DMA transfer.
Module Stop: When the MSTP15 bit in MSTPCR is set to 1, the DMAC clock stops, and the
module stop state is entered. However, 1 cannot be written to the MSTP15 bit if any of the
DMAC channels is enabled. This setting should therefore be made when DMAC operation is
stopped.
When the DMAC clock stops, DMAC register accesses can no longer be made. Since the
following DMAC register settings are valid even in the module stop state, they should be
invalidated, if necessary, before a module stop.
• Transfer end/break interrupt (DTE = 0 and DTIE = 1)
• TEND pin enable (TEE = 1)
• DACK pin enable (FAE = 0 and SAE = 1)
Medium-Speed Mode: When the DTA bit is 0, internal interrupt signals specified as DMAC
transfer sources are edge-detected.
In medium-speed mode, the DMAC operates on a medium-speed clock, while on-chip supporting
modules operate on a high-speed clock. Consequently, if the period in which the relevant interrupt
source is cleared by the CPU, DTC, or another DMAC channel, and the next interrupt is
generated, is less than one state with respect to the DMAC clock (bus master clock), edge
detection may not be possible and the interrupt may be ignored.
Also, in medium-speed mode, DREQ pin sampling is performed on the rising edge of the medium-
speed clock.
Write Data Buffer Function: When the WDBE bit of BCRL in the bus controller is set to 1,
enabling the write data buffer function, dual address transfer external write cycles or single
address transfers and internal accesses (on-chip memory or internal I/O registers) are executed in
parallel.
• Write Data Buffer Function and DMAC Register Setting
If the setting of a register that controls external accesses is changed during execution of an
external access by means of the write data buffer function, the external access may not be
performed normally. Registers that control external accesses should only be manipulated when
external reads, etc., are used with DMAC operation disabled, and the operation is not
performed in parallel with external access.
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