Table 14.4 Selecting External Request Mode With Rs Bits - Hitachi SH7750 Hardware Manual

Table 14.4 Selecting External Request Mode with RS Bits

RS3 RS2 RS1
0 0 0
1
• External Request Acceptance Conditions
1. When at least one of DMAOR.DME and CHCR.DE is 0, and DMAOR.NMIF,
DMAOR.AE, and CHCR.TE are all 0, if an external request (DREQ: edge-detected) is
input it will be held inside the DMAC until DMA transfer is either executed or canceled.
Since DMA transfer is not enabled in this case (DME = 0 or DE = 0), DMA transfer is not
initiated. DMA transfer is started after it is enabled (DME = 1, DE = 1, DMAOR.NMIF =
0, DMAOR.AE = 0, CHCR.TE = 0).
2. When DMA transfer is enabled (DME = 1, DE = 1, DMAOR.NMIF = 0, DMAOR.AE = 0,
CHCR.TE = 0), if an external request (DREQ) is input, DMA transfer is started.
3. An external request (DREQ) will be ignored if input when CHCR.TE = 1, DMAOR.NMIF
= 1, or DMAOR.AE = 1, or during a power-on reset or manual reset, in deep sleep mode or
standby mode, or while the DMAC is in the module standby state.
4. A previously input external request will be canceled by the occurrence of an NMI interrupt
(DMAOR.NMIF = 1) or address error (DMAOR.AE = 1), or by a power-on reset or
manual reset.
In the SH7750S, it is possible to cancel a previously input external request (DREQ). With
DMAOR.COD set to 1, clear CHCRn.DS to 0 and then drive the DREQ pin high.
On the SH7750R, it is possible to cancel an external request that has been accepted by
external request (DREQ) edge detection by first negating DREQ and then clearing
CHCR.DS from 1 to 0. Afterwards CHCR.DS should be reset to 1 and DREQ asserted.
(The SH7750R has no DMAOR.COD bit, but it is possible to cancel an external request
that has been accepted by external request (DREQ) edge detection, as is the case when the
DMAOR.COD bit of the SH7750S is set to 1.)
• Usage Notes
An external request (DREQ) is detected by a low level or falling edge. Ensure that the external
request (DREQ) signal is held high when there is no DMA transfer request from an external
device after a power-on reset or manual reset.
RS0 Address Mode
0 Dual address
mode
0 Single address
mode
1 Single address
mode
Transfer Source
External memory
or memory-mapped
external device, or
external device with
DACK
External memory
or memory-mapped
external device
External device with
DACK
Rev. 6.0, 07/02, page 513 of 986
Transfer Destination
External memory
or memory-mapped
external device, or
external device with
DACK
External device
with DACK
External memory
or memory-mapped
external device