IDT DMA Controller
External DMA Operations
79RC32438 User Reference Manual
9 - 17
November 4, 2002
Notes
An external peripheral generates a DMA request event by asserting a DMA request (DMAREQNx) input.
The DMAREQNx inputs are GPIO alternate functions (see Chapter 12, General Purpose I/O Controller).
Transfer Request:
When the DMA is configured to operate in transfer request mode, a DMA request
instructs the DMA controller to perform one burst transaction to the external peripheral address in DEVCS.
The size of the burst transfer is selected in the TS field.
The assertion of chip select to the external peripheral acknowledges the DMA request and causes the
external peripheral to negate DMAREQNx. When the external peripheral samples chip select negated, it
may once again assert DMAREQNx. An example of a peripheral-to-memory external DMA operation in
transfer request mode is shown in Figure 9.13
Figure 9.13 External DMA Operation (Transfer Request Mode)
Burst Request:
When the DMA is configured to operate in burst request mode, then the first DMA
request initiates the entire DMA transfer between the external peripheral and memory. An example of a
peripheral-to-memory DMA operation in burst request mode is shown in Figure 9.14.
TS
Transfer Size.
This field specifies the DMA burst transfer size used to access the external
peripheral.
0 - byte
1 - halfword
2 - word
3 - 2 words
4 - 4 words
5 - 6 words
6 - 8 words
7 - 16 words
DMA Request Event
Assertion of DMAREQNx pin.
DMA Done Event
Assertion of DMADONENx pin.
DMA Terminated Event
An external device cannot signal a terminated event.
DMA Transfer Size
Value programmed in the transfer size (TS) field of DEVCMD.
Limitations
The width of the TS field must be greater than or equal to the width of the external
DMA peripheral.
Table 9.3 External DMA Operations
EXTCLK
DMAREQNx
CSNx
Transaction
to Memory
to ExTransaction
to ExTransaction
1
2
3
4
5
6
7
1.
2.
DMA requests data transfer by asserting DMAREQNx
The RC32438 acknowledges DMA request by asserting chip select (CSNx) to external peripheral. DMA control-
ler reads a transfer size data quantity from the external peripheral
External peripheral reacts to acknowledgment of DMA request (i.e., assertion of chip select) by negating
DMAREQNx
DMA controller writes data quantity read from external peripheral to memory
DMA requests next data transfer by asserting DMAREQNx
The RC32438 acknowledges next DMA request by asserting chip select and reading a transfer size data quan-
tity from the external peripheral
External peripheral reacts to acknowledgement of DMA request by negating DMAREQNx.
3.
4.
5.
6.
7.