deveopmen
DMAC
Preliminary Specifications REV.D
Specifications in this manual are tentative and subject to change.
Mitsubishi microcomputers
M16C/80 (100-pin version) group
SINGLE-CHIP 16-BIT CMOS MICROCOMPUTER
86
Figure 1.11.7. DMA transfer example by external factors
BCLK
AAAAAA
AAAAAA
DMA0
AAAAA
AAA
AAAAA
DMA1
DMA0
request bit
DMA1
request bit
AAA
AAAAAA
AAAAAA
AAAAAA
AAAAAA
CPU
INT0
INT1
In this example, DMA transfer request signals are input simultaneously from
external factors and the DMA transfers are executed in the minimum cycles.
Bus
priviledge
acquired
(1) Internal factors
The DMAi request flag is set to “1” in response to internal factors at the same time as the interrupt
request bit of the interrupt control register for each factor is set. This is because, except for software
trigger DMA factors, they use the interrupt request signals output by each function.
The DMAi request bit is cleared to "0" when the DMA transfer starts or the DMA transfer is in disable
state (channel i transfer mode select bits are "00" and the DMAi transfer count register is "0").
(2) External factors
These are DMA request factors that are generated by the input edge from the INTi pin (where i indi-
cates the DMAC channel). When the INTi pin is selected by the DMAi request factor select bit as an
external factor, the inputs from these pins become the DMA request signals.
When an external factor is selected, the DMAi request bit is set, according to the function specified in the
DMA request factor select bit, on either the falling edge of the signal input via the INTi pins, or both edges.
When an external factor is selected, the DMAi request bit is cleared, in the same way as the DMAi
request bit is cleared for internal factors, when the DMA transfer starts or the DMA transfer is in
disable state.
(3) Relationship between external factor request input and DMAi request flag, and DMA transfer timing
When the request inputs to DMAi occur in the same sampling cycle (between the falling edge of BCLK
and the next falling edge), the DMAi request bits are set simultaneously, but if the DMAi enable bits
are all set, DMA0 takes priority and the transfer starts. When one transfer unit is complete, the bus
privilege is returned to the CPU. When the CPU has completed one bus access, DMA1 transfer starts,
and, when one transfer unit is complete, the privilege is again returned to the CPU.
The priority is as follows: DMA0 > DMA1 > DMA2 > DMA3.
Figure 1.11.7. DMA transfer example by external factors shows what happens when DMA0 and DMA1
requests occur in the same sampling cycle.