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5.16 IDMA PINS OR PORT A PINS
Each of these three pins can be used either as dedicated pins for the IDMA
signals or as general-purpose parallel 1/0 port A pins. Note that even if one
or more of the IDMA pins are used as general-purpose 1/0 pins, the IDMA
can still be used. For example, if DONE is not needed by the IDMA, it can be
configured as a general-purpose 1/0 pin. If the IDMA is used for memory-to-
memory transfers only, then all three pins can be used as general-purpose
1/0 pins.
DREQ/PA13 -
OMA Request
This input is asserted by a peripheral device to request an operand transfer
between that peripheral device and memory. In the cycle steal request
generation mode, this input is edge-sensitive. In burst mode, it is level-
sensitive.
DACK/PA14- OMA Acknowledge
This output, asserted by the IDMA, signals to the peripheral that an operand
is being transferred in response to a previous transfer request.
DONE/PA 15 - DONE
This bidirectional, open-drain signal is asserted by the IDMA or by a pe-
ripheral device during any IDMA bus cycle, to indicate that the data being
transferred is the last item in a block. The IDMA asserts this signal as an
output during a bus cycle when the byte count register is decremented to
zero.
5.17 IACK OR PIO PORT B PINS
5-16
Each one of these three pins can be used either as a dedicated interrupt
acknowledge signal or as a general-purpose parallel 1/0 port. Note that the
IMP interrupt controller does not require the IACK pins to support the three
dedicated mode interrupt levels.
IACK7/PBO
IACK6/PB1
IACK1/PB2 - Interrupt Acknowledge/Port B 1/0
As IACK1, IACK6, and IACK7, these active low output signals indicate to
the external device that the MC68302 is executing an interrupt acknowledge
cycle. The external device must then place its vector number on the lower
byte of the data bus or use AVEC for autovectoring.
MC68302 USER'S MANUAL
MOTOROLA
I,
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