Mitsubishi microcomputers
M16C / 61 Group
DMAC
SINGLE-CHIP 16-BIT CMOS MICROCOMPUTER
Table 1.15.1. DMAC specifications
Item
No. of channels
Transfer memory space
Specification
2 (cycle steal method)
• From any address in the 1M bytes space to a fixed address
• From a fixed address to any address in the 1M bytes space
• From a fixed address to a fixed address
(Note that DMA-related registers [002016 to 003F16] cannot be accessed)
Maximum No. 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 INT1 (INT0 can be selected by DMA0, INT1 by DMA1)
Timer A0 to timer A4 interrupt requests
Timer B0 to timer B2 interrupt requests
UART0 transmission and reception interrupt requests
UART1 transmission and reception interrupt requests (UART1 trans-
mission can be selected by DMA0, UART1 reception by DMA1)
UART2 transmission and reception interrupt requests
A-D conversion interrupt requests
Software triggers
Channel priority
DMA0 takes precedence if DMA0 and DMA1 requests are generated simultaneously
8 bits or 16 bits
Transfer unit
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 bit turns to
“0”, and the DMAC turns 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 DMAC is active.
When the DMAC is active, data transfer starts every time a 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
At the time of starting data transfer immediately after turning the DMAC active, re
the value of one of source pointer and destination pointer - the one specified for the
forward direction - is reloaded to the forward direction address pointer,and the value
of the transfer counter reload register is reloaded to the transfer counter.
Registers specified for forward direction transfer are always write enabled.
Registers specified for fixed address transfer are write-enabled when
the DMA enable bit is “0”.
Forward address pointer and
load timing for transfer
counter
Writing to register
Reading the register
Can be read at any time.
However, when the DMA enable bit is “1”, reading the register set up as the
forward register is the same as reading the value of the forward address pointer.
Note: DMA transfer is not effective to any interrupt. DMA transfer is affected neither by the interrupt enable
flag (I flag) nor by the interrupt priority level.
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MITSUBISHI [ Mitsubishi Group ]
