
1-61
Under
development
Specifications in this manual are tentative and subject to change
Rev. H
Direct Memory Access Controller
MITSUBISHI MICROCOMPUTERS
M30222 Group
SINGLE-CHIP 16-BIT CMOS MICROCOMPUTER
Table 1.23. DMAC specifications
Note: DMA transfers do not effect any interrupt and are not affected by the interrupt enable flag (I flag) or by any interrupt
priority level.
Item
Specification
Number of channels
2 (cycle-stealing method)
Transfer memory space
From any address in the 1m byte space to a fixed address
From a fixed address to any address in the 1 M byte space
From a fixed address to a fixed address
DMA-related registers (002016 to 003F16) cannot be accessed
Maximum number of bytes transferred
128K bytes (with 16-bit transfers) or 64K bytes (with 8-bit transfers)
DMA request factors (Note)
Falling edge of INT0 or INT1or both edges
(INT0 can be selected by DMA0, INT1 by DMA1)
Timer A0 to Timer A4 interrupt requests
Timer B0 to Timer B5 interrupt requests
UART0 transfer and receive interrupt requests
UART1 transfer and receive interrupt requests
UART2 transfer and receive interrupt requests
Serial I/O 3,4 interrupt requests
A-D conversion interrupt requests
Software triggers
Channel priority
DMA0 has priority if DMA0 and DMA1 requests are generated simultaneously
Transfer unit
8 bit or 16 bit
Transfer address direction
Forward/Fixed
(Forward direction cannot be specified for both source and destination
simultaneously)
Transfer mode
Single transfer mode
After the transfer counter underflows, the DMA enable becomes 0 and the
DMAC becomes inactive.
Repeat transfer mode
After the transfer counter underflows, the value of the transfer counter
reload register is reloaded to the transfer counter. The DMAC remains
active unless a 0 is written to the DMA enable bit.
DMA interrupt request generation timing
When an underflow occurs in the transfer counter
Active
When the DMA enable bit is set to 1 , the DMA is active.
When the DMA is active, data transfer starts each time the DMA transfer
request signal occurs.
Inactive
When the DMA enable bit is set to 0 , the DMAC is inactive.
After the transfer counter underflows in single transfer mode.
Forward address pointer and reload timing
for transfer counter
When the DMAC is enabled, the DMA source pointer is loaded to the DMA forward
address pointer. The DMA transfer load pointer is copied to the DMA transfer
counter at that time.
Writing to register
Registers specified for forward direction transfer are always write enabled. Regis-
ters specified for fixed address transfer are write enabled when the DMA enable bit
is 0 .
Reading the register
Can be read anytime. However, when the DMA enable bit is 1 , reading the regis-
ter set up as the forward register is the same as reading the value of the forward
address pointer.