337
15.6 DMAC Transfer Modes
Burst Transfer Mode
1. The initi alization routine sets the descriptor.
2. The program initializes the DMA transfer request source. To use the internal peripheral
circuit as the transfer request source, enable interrupt request s and disable inte rrupts in the
ICR of the interrupt controller.
3. The program sets the target DOEn bit of the DACSR to 1.
--- This completes the setting for DMA. ---
4. Upon det ection of a DMA transfer request input, the DM AC requests bus control right from
the CPU.
5. When th e bus control right is transferred fr om the CPU, t he DMAC acces ses three wo rds of
information of the descriptor through the bus.
6. While de crem enting DMACT, th e DMAC performs a tr ansfer bas ed on the informati on stored
in the descriptor as many times as specified by DMACT. The DMAC outputs a transfer
request acknowledgment signal during data transfer (if externa l transfer request input is
used). When the decremented DMACT reaches 0, the DMAC outputs a transfer end si gnal
during data transfer.
7. The DMAC increments or decrements SADR or DADR and writes the result together with the
DMACT value back to the descriptor.
8. The DMAC returns the bus control right to the CPU.
9. The DMAC sets DACS R DEDn to 1 and causes an interrupt to the CPU if interrupts have
been enabled.
The number of minimum required cycles per transfer is shown below (on the assumption that
the descriptor is stored in built-in RAM, data is tr ansferred between external busses an d the
data length is counted in bytes):
When bot h transfer source and destination addresses are fixed: (6 + 5 × n) cycles
When ei ther the transfer source or destination address is fixed: (7 + 5 × n) cycles
When bot h tran sfer source an d destin atio n addr esses are i ncremen ted or decr emente d: (8 +
5 × n) cycles