Dma Transfer Requests - Hitachi SH7032 Hardware Manual

9.3.2

DMA Transfer Requests

DMA transfer requests are basically generated in either the data transfer source or destination, but
they can also be generated by devices and on-chip supporting modules that are neither the source
nor the destination. Transfers can be requested in three modes: auto-request, external request, and
on-chip module request. The request mode is selected with the RS3–RS0 bits in the DMA channel
control registers 0–3 (CHCR0–CHCR3).
Auto-Request Mode: When there is no transfer request signal from an external source, as in a
memory-to-memory transfer or a transfer between memory and an on-chip supporting module
unable to request a transfer, the auto-request mode allows the DMAC to automatically generate a
transfer request signal internally. When the DE bits in CHCR0–CHCR3 and the DME bit in
DMAOR are set to 1, the transfer begins (so long as the TE bits in CHCR0–CHCR3 and the NMIF
and AE bits in DMAOR are all 0).
External Request Mode: In this mode a transfer is performed in response to a request signal
(DREQ) of an external device. Choose one of the modes shown in table 9.3 according to the
application system. When this mode is selected, if DMA transfer is enabled (DE = 1, DME = 1,
TE = 0, NMIF = 0, AE = 0), a transfer is performed upon a request at the DREQ input. Choose to
detect DREQ by either the falling edge or low level of the signal input with the DS bit in CHCR0–
CHCR3 (DS = 0 specifies level detection, DS = 1 specifies edge detection). The source of the
transfer request does not have to be the data transfer source or destination.
Table 9.3 Selecting External Request Modes with the RS Bits
RS3 RS2 RS1
0 0 0
0 0 1
0 0 1
Note: * External memory, memory-mapped external device, on-chip memory, on-chip supporting
module (excluding DMAC)
On-Chip Module Request: In this mode a transfer is performed in response to a transfer request
signal (interrupt request signal) of an on-chip module. The transfer request signals include the
receive data full interrupt (RXI) of the serial communication interface (SCI), the transmit data
empty interrupt (TXI) of the SCI, the input capture A/compare match A interrupt request (IMIA)
of the 16-bit integrated pulse timer (ITU), and the A/D conversion end interrupt (ADI) of the A/D
converter (table 9.4). When this mode is selected, if DMA transfer is enabled (DE = 1, DME = 1,
TE = 0, NMIF = 0, AE = 0), a transfer is performed upon input of a transfer request signal. The
190
RS0 Address Mode
0 Dual address
mode
0 Single address
mode
1 Single address
mode
Source
Any *
External memory or
memory-mapped
external device
External device with
DACK
Destination
Any *
External device with
DACK
External memory or
memory-mapped
external device