
Rev. 2.0, 09/02, page 185 of 732
10.4.8
DMAC Access from CPU
The space addressed by the DMAC is 3-cycle space. Therefore, when the CPU becomes the bus
master and accesses the DMAC, a minimum of three system clock (
φ
) cycles are required for one
bus cycle. Also, since the DMAC is located in word space, while a word-size access to the DMAC
is completed in one bus cycle, a longword-size access is automatically divided into two word
accesses, requiring two bus cycles (six basic clock cycles). These two bus cycles are executed
consecutively; a different bus cycle is never inserted between the two word accesses. This applies
to both write accesses and read accesses.
10.5
Examples of Use
10.5.1
Example of DMA Transfer between On-Chip SCI and External Memory
In this example, on-chip serial communication interface channel 0 (SCI0) received data is
transferred to external memory using the DMAC channel 3.
Table 10.6 indicates the transfer conditions and the setting values of each of the registers.
Table 10.6 Transfer Conditions and Register Set Values for Transfer between On-chip SCI
and External Memory
Transfer Conditions
Transfer source: RDR0 of on-chip SCI0
Transfer destination: external memory
Transfer count: 64 times
Transfer source address: fixed
Transfer destination address: incremented
Transfer request source: SCI0 (RDR0)
Bus mode: cycle steal
Transfer unit: byte
Interrupt request generation at end of transfer
Channel priority ranking: 0
>
1
>
2
>
3
Register
SAR_3
DAR_3
DMATCR_3
CHCR_3
Value
H'FFFF81A5
H'00400000
H'00000040
H'00004D05
DMAOR
H'0001