Datasheet

M16C/6S Group DMAC
R01DS0201EJ0502 Rev.5.02 page 68 of 203
Dec 25, 2012
DMAC
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 1.11.1 shows the block diagram of the DMAC. Table 1.11.1
shows the DMAC specifications. Figures 1.11.2 to 1.11.4 show the DMAC-related registers.
Figure 1.11.1. 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) (Note)
Data bus high-order bits
Address bus
DMA1 destination pointer DAR1 (20)
DMA1 source pointer SAR1 (20)
DMA1 forward address pointer (20) (Note)
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 002916, 002816)
(addresses 0039
16, 003816)
(addresses 0022
16 to 002016)
(addresses 0026 16 to 0024 16 )
(addresses 003216 to 003016)
(addresses 0036 16 to 0034 16 )
Note: Pointer is incremented by a DMA request.
A DMA request is generated by a write to the DMiSL register (i = 0–1)’s DSR bit, as well as by an interrupt
request which is generated by any function specified by the DMiSL register’s DMS and DSEL3–DSEL0 bits.
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 interrupt control register’s IR bit does not change state due to a DMA transfer.
A data transfer is initiated each time a DMA request is generated when the DMiCON register’s DMAE bit =
“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 “DMA Requests”.