MC68030 Datasheet, PDF (78/602 Pages) Motorola, Inc – ENHANCED 32-BIT MICROPROCESSOR

Data Organization and Addressing Capabilities
To implement growth of the queue from high to low memory, use:
–(An) to put data into the queue,
–(Am) to get data from the queue.
After a "put'' operation, the "put'' address register points to the last item place din the queue,
and the unchanged "get'' address register points to the last item removed from the queue.
After a "get'' operation, the "get'' address register points to the last item removed from the
queue, and the unchanged "put'' address register points to the last item placed in the queue.
This is illustrated as:
PUT - (An)
LOW MEMORY
(FREE)
LAST PUT
GET - (Am)
NEXT GET
LAST GET (FREE)
HIGH MEMORY
To implement the queue as a circular buffer, the "get'' or "put'' operation should be
performed first, and then the relevant address register should be checkout and adjusted, if
necessary. The address register is adjusted by adding the buffer length (in bytes) to the
register contents.
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MC68030 USER’S MANUAL
MOTOROLA