![](http://datasheet.mmic.net.cn/90000/M37641M8-XXXHP_datasheet_3496247/M37641M8-XXXHP_219.png)
Rev.2.00
Aug 28, 2006
page 88 of 148
7641 Group
REJ09B0336-0200
APPLICATION
2.5 DMAC
2.5.3 DMAC operation description
The DMAC transfers data using the bus without use of the CPU. The DMAC consists of DMAC0 and
DMAC1, which have the same function each.
There are two transfer modes: Burst transfer mode or Cycle steal transfer mode.
Burst transfer mode
Once a DMA transfer request is accepted, an entire batch of data is transferred. The right to use bus is
not returned to the CPU until the transfer of all data has been completed.
The DMAC transfers the number of bytes data specified by the transfer count register for each request.
The count register is a 16-bit counter; the maximum number of data is 65,536 bytes per one request.
Cycle steal mode
The DMAC transfers one byte of data for each request. If one byte transfer has been completed and then
a DMA transfer request is not generated, the right to use bus is returned to the CPU.
Figure 2.5.11 shows the transfer mode overview.
s Burst transfer mode
CPU
DMACx request is accepted.
DMACx (x = 0, 1)
(Transfer of entire batch of data)
CPU
DMAC0
CPU
s Cycle steal transfer mode
CPU
DMAC0
DMAC1
Right to use bus
CPU
Right to use bus
DMAC0 request is accepted.
DMAC0 request
is accepted.
DMAC1 request
is accepted.
(One-byte transfer)
(One-byte transfer)(One-byte transfer)
Fig. 2.5.11 Transfer mode overview
(1) Priority
The DMAC places a higher priority on Channel-0 transfer requests than on Channel-1 transfer
requests.
If a channel-0 transfer request occurs during a channel-1 burst transfer operation, the DMAC completes
the next transfer source and destination read/write operation first, and then starts the channel-0
transfer operation. As soon as the channel-0 transfer is completed, the DMAC resumes the channel-
1 transfer operation.
(2) Transfer request acceptance
A transfer request is confirmed at every rising of
φ. After that a channel priority and a right to use
the bus is judged.
A software trigger and/or a hardware factor can be selected as a transfer request source. The DMAC
channel x hardware transfer request source bits (DxHR) selects a hardware factor.
Writing “1” to the DMAC channel x software transfer trigger bit (DxSWT) can generate a transfer
request as a software trigger.