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DMAC
Preliminary Specifications REV.B
Specifications in this manual are tentative and subject to change.
Mitsubishi microcomputers
M16C/80 (144-pin version) group
SINGLE-CHIP 16-BIT CMOS MICROCOMPUTER
77
DMAC
This microcomputer has four DMAC (direct memory access controller) channels that allow data to be sent
to memory without using the CPU. DMAC is a function that to transmit 1 data of a source address (8 bits /
16 bits) to a destination address when transmission request occurs. When using three or more DMAC
channels, the register bank 1 register and high-speed interrupt register are used as DMAC registers. If you
are using three or more DMAC channels, you cannot, therefore, use high-speed interrupts. The CPU and
DMAC use the same data bus, but the DMAC has a higher bus access privilege than the CPU, and because
of the use of cycle-steeling, operations are performed at high-speed from the occurrence of a transfer
request until one word (16 bits) or 1 byte (8 bits) of data have been sent. Figure 1.11.1 shows the mapping
of registers used by the DMAC.
Table 1.11.1 shows DMAC specifications. Figures 1.11.2 to 1.11.5 show the
structures of the registers used.
As the registers shown in Figure 1.11.1 is allocated in CPU, use LDC instruction when writing. When writing
to DCT2, DCT3, DRC2, DRC3, DMA2 and DMA3, set register bank select flag (B flag) to "1" and use MOV
instruction to set R0 to R3, A0 and A1 registers. When writing to DSA2 and DSA3, set register bank select
flag (B flag) to "1" and use LDC instruction to set SB and FB registers.
DMA mode register
DMA transfer count register
DMA transfer count reload register
DMA memory address register
DMA SFR address register
DMA memory address reload register
DMD0
DMD1
DCT0
DCT1
DRC0
DRC1
DMA0
DMA1
DSA0
DSA1
DRA0
DRA1
DMAC related register
When using three or more DMAC register channels
The high-speed interrupt register is used as a DMAC
register
DMA2 transfer count register
DMA2 transfer count reload register
DMA2 memory address register
DMA2 SFR address register
DCT2 (R0)
DCT3 (R1)
DRC2 (R2)
DRC3 (R3)
DMA2 (A0)
DMA3 (A1)
DSA2 (SB)
DSA3 (FB)
When using DMA2 and DMA3, use the CPU
registers shown in parentheses.
When using three or more DMAC channels
The register bank is used as a DMAC register
DMA3 transfer count register
DMA3 transfer count reload register
DMA3 memory address register
DMA3 SFR address register
SVF
DMA2 memory address reload register
DRA2 (SVP)
DRA1 (VCT)
Flag save register
DMA3 memory address reload register
Figure 1.11.1. Register map using DMAC
In addition to writing to the software DMA request bit to start DMAC transfer, the interrupt request signals
output from the functions specified in the DMA request factor select bits are also used. However, in contrast
to the interrupt requests, repeated DMA requests can be received, regardless of the interrupt flag.
(Note, however, that the number of actual transfers may not match the number of transfer requests if the
DMA request cycle is shorter than the DMR transfer cycle. For details, see the description of the DMAC
request bit.) see the description of the DMAC request bit.