Datasheet

11. DMAC
page 82
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11. DMAC
Note
Do not use UART0 transfer and UART0 reception interrupt request as a DMA request in the 42-pin
package.
The DMAC (Direct Memory Access Controller) allows data to be transferred without the CPU intervention.
Two DMAC channels are included. Each time a DMA request occurs, the DMAC transfers one (8 or 16-bit)
data from the source address to the destination address. The DMAC uses the same data bus as used by
the CPU. Because the DMAC has higher priority of bus control than the CPU and because it makes use of
a cycle steal method, it can transfer one word (16 bits) or one byte (8 bits) of data within a very short time
after a DMA request is generated. Figure 11.1 shows the block diagram of the DMAC. Table 11.1 shows the
DMAC specifications. Figures 11.2 to 11.4 show the DMAC-related registers.
A DMA request is generated by a write to the DSR bit in the DMiSL register (i = 0,1), as well as by an
interrupt request which is generated by any function specified by the DMS and DSEL3 to DSEL0 bits in the
DMiSL register. However, unlike in the case of interrupt requests, DMA requests are not affected by the I
flag and the interrupt control register, so that even when interrupt requests are disabled and no interrupt
request can be accepted, DMA requests are always accepted. Furthermore, because the DMAC does not
affect interrupts, the IR bit in the interrupt control register does not change state due to a DMA transfer.
A data transfer is initiated each time a DMA request is generated when the DMAE bit in the DMiCON
register is set to “1” (DMA enabled). However, if the cycle in which a DMA request is generated is faster
than the DMA transfer cycle, the number of transfer requests generated and the number of times data is
transferred may not match. For details, refer to 11.4 DMA Requests.
Figure 11.1 DMAC Block Diagram
Data bus low-order bits
DMA latch high-order bits DMA latch low-order bits
DMA0 source pointer SAR0(20)
DMA0 destination pointer DAR0 (20)
DMA0 forward address pointer (20)
(1)
Data bus high-order bits
Address bus
DMA1 destination pointer DAR1 (20)
DMA1 source pointer SAR1 (20)
DMA1 forward address pointer (20)
(1)
DMA0 transfer counter reload register TCR0 (16)
DMA0 transfer counter TCR0 (16)
DMA1 transfer counter reload register TCR1 (16)
DMA1 transfer counter TCR1 (16)
(addresses 0029 16 , 0028 16 )
(addresses 0039
16 , 0038 16 )
(addresses 0022
16 to 0020 16 )
(addresses 0026 16 to 0024 16 )
(addresses 0032 16 to 0030 16 )
(addresses 0036 16 to 0034 16 )
NOTE:
1. Pointer is incremented by a DMA request.