Analog Devices adsp-2100 Manual page 142

If the processor is free to handle the autobuffer requests in the order they
are generated, the receive autobuffer happens first and is then followed by
the transmit autobuffer. The order of these operations may change if the
processor is not available to handle the requests due to any of the
previously mentioned latencies. In this case there are 1
between the requests. If the processor is subject to bus requests, wait
states, or other latencies which are longer than 1
autobuffer operations may be held off. Since the transmit autobuffer has a
higher priority, it's request will occur first. Because of the priority of the
autobuffer requests the use of a single I register more difficult or even
impossible in some cases. As long as there are no possible latency cases
longer than the difference in the timing of the requests, it is quite possible
to use a single I register for serial port autobuffering.
Serial Ports
1 ⁄ serial clock cycles
2
1 ⁄ serial clock cycles, both
2
5
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