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MC68341 USER'S MANUAL
MOTOROLA
same size, two cycles will transfer the complete operand. If the source and destination
operands are different sizes, the number of cycles will vary. If the source is a long-word and
the destination is a byte, there would be one bus cycle for the read and four bus cycles for
the write. Once the DMA channel has started a dual-address operand transfer, it must
complete that transfer before releasing ownership of the bus or servicing a request for
another channel of equal or higher priority, unless one of the bus cycles is terminated with
a bus error during the transfer.
6.6.3 Channel Termination
The channel can terminate by normal completion or as the result of an error. The status of
a DMA operation can be determined by reading the CSR. The DMA channel can also
interrupt the processor to inform it of errors, normal transfer completion, or breakpoints.
The fast termination option can also be used to provide a two-clock access for external
requests.
6.6.3.1 CHANNEL TERMINATION. The channel operation can be terminated for several
reasons: the BTC is decremented to zero, a peripheral device asserts DONE≈ during an
operand transfer, the STR bit is cleared in the CCR, a bus cycle is terminated with a bus
error, or a reset occurs.
6.6.3.2 INTERRUPT OPERATION. Interrupts can be generated by error termination of a
bus cycle or by normal channel completion. Specifically, if the CCR interrupt error (INTE)
bit is set and a bus error on source (CCR BES) bit, bus error on destination (CCR BED) bit,
or configuration error (CCR CONF) bit is set, the CCR IRQ bit is set. In this case, clearing
the INTE, BES, BED, or CONF bits causes the IRQ bit to be cleared. If the interrupt normal
(CCR INTN) bit is set and the CCR DONE bit is set, the IRQ bit is set. In this case, clearing
the INTN or the DONE bit causes the IRQ bit to be cleared. If the interrupt breakpoint (CCR
INTB) and the CSR BRKP bits are set, the IRQ bit is set. Clearing INTB or BRKP clears
IRQ.
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Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
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