Motorola PowerQUICC II MPC8280 Series Reference Manual page 692

IDMA Interface Signals
19.7.1.1 Level-Sensitive Mode
For external devices requiring very high data transfer rates, level-sensitive mode allows the
IDMA to use a maximum bandwidth to service the device. The device requests service by
asserting DREQx and leaving it asserted as long as it needs service. This mode is selected
by setting the corresponding RCCR[DRxM].
The IDMA asserts DACK each time it issues a bus transaction to either read or write the
peripheral. The peripheral must use TA and TEA for data validation. DACK is the
acknowledgment of the original burst request given on DREQx. DREQx should be negated
during the DACK active period to ensure that no further transactions are performed.
19.7.1.2 Edge-Sensitive Mode
For external devices that generate a pulsed signal for each operand to be transferred,
edge-sensitive mode should be used. In edge-sensitive mode, the IDMA controller moves
one operand for each falling/rising (as configured by RCCR[EDMx]) edge of DREQx. This
mode is selected by clearing the corresponding RCCR[DRxM] and programming the
corresponding RCCR[EDMx] to the proper edge.
When the IDMA controller detects a valid edge on DREQx, a request becomes pending and
remains pending until it is serviced by the IDMA. Subsequent changes on DREQx are
ignored until the request begins to be serviced. The servicing of the request results in one
operand being transferred. Each time the IDMA issues a bus transaction to either read or
write the device, the IDMA asserts DACK. The device must use TA and TEA for data
validation. Thus, DACK is the acknowledgment of the original transaction request given on
DREQx.
19.7.2 DONEx
This bidirectional open-drain signal is used to indicate the last IDMA transfer. DONE can
be an output of the IDMA in the source or destination bus transaction if the transfer count
is exhausted. This function is controlled by BD[SDN, DDN].
DONE can also operate as an input. When operating in external request modes, DONE may
be used as an input to the IDMA controller to indicate that the device being serviced
requires no more transfers. In that case, the transfer is terminated, the current BD is closed,
and an interrupt is generated (if enabled).
DONE is ignored if it is asserted externally during internal
request mode (DCM[ERM] = 0).
DONE
memory-to-memory transfers if external request mode is
enabled (DCM[ERM] = 1).
19-16
Freescale Semiconductor, Inc.
NOTE
must not be
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asserted externally during
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