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DMA Controller Module Functional Description
external request is initiated by asserting DREQn while DCRn[EEXT] is set. Note
that multiple transfers will occur if DREQn is continuously asserted.
• Continuous mode (DCRn[CS] = 0)—After an internal or external request, the DMA
continuously transfers data until BCRn reaches zero or a multiple of DCRn[BWC]
or until DSRn[DONE] is set. If BCRn is a multiple of BWC, the DMA request signal
is negated until the bus cycle terminates to allow the internal arbiter to switch
masters. DCRn[BWC] = 000 specifies the maximum transfer rate; other values
specify a transfer rate limit.
The DMA performs the specified number of transfers, then relinquishes bus control.
The DMA negates its internal bus request on the last transfer before BCRn reaches
a multiple of the boundary specified in BWC. On completion, the DMA reasserts its
bus request to regain mastership at the earliest opportunity. The DMA loses bus
control for a minimum of one bus cycle.
16.5.2 Data Transfer Modes
Each channel supports dual-address transfers, described in the next section.
16.5.2.1 Dual-Address Transfers
Dual-address transfers consist of a source data read and a destination data write. The DMA
controller module begins a dual-address transfer sequence during a DMA request. If no
error condition exists, DSRn[REQ] is set.
• Dual-address read—The DMA controller drives the SARn value onto the internal
address bus. If DCRn[SINC] is set, the SARn increments by the appropriate number
of bytes upon a successful read cycle. When the appropriate number of read cycles
complete (multiple reads if the destination size is larger than the source), the DMA
initiates the write portion of the transfer.
If a termination error occurs, DSRn[BES,DONE] are set and DMA transactions
stop.
• Dual-address write—The DMA controller drives the DARn value onto the address
bus. If DCRn[DINC] is set, DARn increments by the appropriate number of bytes at
the completion of a successful write cycle. BCRn decrements by the appropriate
number of bytes. DSRn[DONE] is set when BCRn reaches zero. If the BCRn is
greater than zero, another read/write transfer is initiated. If the BCRn is a multiple
of DCRn[BWC], the DMA request signal is negated until termination of the bus
cycle to allow the internal arbiter to switch masters.
If a termination error occurs, DSRn[BES,DONE] are set and DMA transactions
stop.
16-12
MCF5282 User's Manual
MOTOROLA
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