M16C30L Datasheet, PDF (67/166 Pages) Renesas Technology Corp – SINGLE-CHIP 16-BIT CMOS MICROCOMPUTER

DMAC
Mitsubishi microcomputers
M16C / 30L Group
SINGLE-CHIP 16-BIT CMOS MICROCOMPUTER
DMAC
This microcomputer has one DMAC (direct memory access controller) channel that allow data to be sent to
memory without using the CPU. DMAC shares the same data bus with the CPU. The DMAC is given a
higher right of using the bus than the CPU, which leads to working the cycle stealing method. On this
account, the operation from the occurrence of DMA transfer request signal to the completion of 1-word (16-
bit) or 1-byte (8-bit) data transfer can be performed at high speed. Figure 1.13.1 shows the block diagram
of the DMAC. Table 1.13.1 shows the DMAC specifications. Figures 1.13.2 to 1.13.4 show the registers
used by the DMAC.
Address bus
DMA0 transfer counter reload register TCR0 (16)
(addresses 002916, 002816)
DMA0 transfer counter TCR0 (16)
DMA0 source pointer SAR0(20)
(addresses 002216 to 002016)
DMA0 destination pointer DAR0 (20)
(addresses 002616 to 002416)
DMA0 forward address pointer (20) (Note)
DMA latch high-order bits DMA latch low-order bits
Data bus low-order bits
Data bus high-order bits
Figure 1.13.1. Block diagram of DMAC
Note: Pointer is incremented by a DMA request.
Either a write signal to the software DMA request bit or an interrupt request signal is used as a DMA transfer
request signal. But the DMA transfer is affected neither by the interrupt enable flag (I flag) nor by the
interrupt priority level. The DMA transfer doesn't affect any interrupts either.
If the DMAC is active (the DMA enable bit is set to 1), data transfer starts every time a DMA transfer request
signal occurs. If the cycle of the occurrences of DMA transfer request signals is higher than the DMA
transfer cycle, there can be instances in which the number of transfer requests doesn't agree with the
number of transfers. For details, see the description of the DMA request bit.
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