DMAC
9
9.3 Functional Description of the DMAC
9.3.6 Transfer Units
Use the TSZSL (DMA transfer size select) bit to set for each channel the number of bits (8 or 16 bits) to be
transferred in one DMA transfer.
9.3.7 Transfer Counts
Use the DMA Transfer Count Register to set transfer counts for each channel. Transfer can be performed up to
65,536 times. The value of the DMA Transfer Count Register is decremented by one every time one transfer unit
is transferred. In ring buffer mode, the DMA Transfer Count Register operates in free-run mode, with the value
set in it ignored.
9.3.8 Address Space
The address space in which data can be transferred by DMA is 64 Kbytes of internal peripheral I/O or RAM space
(H’0080 0000 through H’0080 FFFF) for both source and destination. To set the source and destination addresses on
each DMA channel, use the DMA Source Address Register and DMA Destination Address Register.
9.3.9 Transfer Operation
(1) Dual-address transfer
Irrespective of the size of transfer unit, data is transferred in two bus cycles, one for source read access and
one for destination write access. (The transfer data is taken into the DMAC’s internal temporary register
before being transferred.)
(2) Bus protocol and bus timing
Because the bus interface is shared with the CPU, DMA transfer is performed with the same bus protocol and
the same bus timing as when peripheral modules are accessed by the CPU.
(3) Transfer rate
Transfer is performed using a total of three peripheral clock cycles, one cycle to gain control of the bus and
one read and one write cycle to perform one transfer. Therefore, the maximum transfer rate is calculated by
the equation below:
1
Maximum transfer rate [bytes per second] = 2 bytes ×
1/f(BCLK) × 3 cycles
(4) Address count direction and address changes
The direction in which the source and destination addresses are counted as transfer proceeds (“Address
fixed” or “Address incremental”) is set for each channel using the SADSL (source address direction select)
and DADSL (destination address direction select) bits.
When the transfer size is 16 bits, the address is incremented by two for each DMA transfer performed; when
the transfer size is 8 bits, the address is incremented by one.
Table 9.3.11 Address Count Direction and Address Changes
Address Count Direction
Address fixed
Transfer Unit
8 bits
Address Change for One DMA
0
0
16 bits
Address incremental
8 bits
+1
+2
16 bits
32180 Group User’s Manual (Rev.1.0)
9-35
RENESAS [ RENESAS TECHNOLOGY CORP ]
