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15.6 DMAC Transfer Modes
15.6 DMAC Transfer Modes

The DMAC supports the following three transfer modes:

This section explains the operation in these modes.

Single/block transfer mode

Continuous transfer mode

Burst transfer mode

Single/Block 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 BLK or until DMACT reaches 0. The DMAC
outputs a transfer request acknowledgment signal du ring data transfer (if external tran sfer
request input is used). When decremented DMACT reaches 0, the DMAC outputs a tran sfer
end signal during data transfer.
7. The DMAC clears the transfer request input.
8. The DMAC increments or decrements SADR or DADR and writes the result together with the
DMACT value back to the descriptor.
9. The DMAC returns the bus control right to the CPU.
10.If the DMACT value is 0, the DMAC sets DACSR 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 transferred between exter nal busses, and the
data length is counted in bytes):
When bot h transfer source and destination addresses are fixed: (6 + 5 × B LK) cycles
When one of the transfer source and destination addresses is fixed: (7 + 5 × BLK) cycles
When bot h tran sfer source an d destin atio n addr esses are i ncremen ted or decr emente d: (8 +
5 × BLK) cycles