37C957FR Datasheet, PDF (139/328 Pages) SMSC Corporation – ULTRA I/O CONTROLLER FOR PORTABLE APPLICATIONS

Note: A threshold of 16 is equivalent to a threshold of 15. These two cases are treated the same.
Programmed I/O - Transfers from the FIFO to the Host
In the reverse direction an interrupt occurs when serviceIntr is 0 and readIntrThreshold bytes are
available in the FIFO. If at this time the FIFO is full it can be emptied completely in a single burst,
otherwise readIntrThreshold bytes may be read from the FIFO in a single burst.
readIntrThreshold =(16-<threshold>) data bytes in FIFO
An interrupt is generated when serviceIntr is 0 and the number of bytes in the FIFO is greater than or
equal to (16-<threshold>). (If the threshold = 12, then the interrupt is set whenever there are 4-16
bytes in the FIFO.) The PINT pin can be used for interrupt-driven systems. The host must respond
to the request by reading data from the FIFO. This process is repeated until the last byte is
transferred out of the FIFO. If at this time the FIFO is full, it can be completely emptied in a single
burst, otherwise a minimum of (16-<threshold>) bytes may be read from the FIFO in a single burst.
Programmed I/O - Transfers from the Host to the FIFO
In the forward direction an interrupt occurs when serviceIntr is 0 and there are writeIntrThreshold or
more bytes free in the FIFO. At this time if the FIFO is empty it can be filled with a single burst
before the empty bit needs to be re-read. Otherwise it may be filled with writeIntrThreshold bytes.
writeIntrThreshold =
(16-<threshold>) free bytes in FIFO
An interrupt is generated when serviceIntr is 0 and the number of bytes in the FIFO is less than or
equal to <threshold>. (If the threshold = 12, then the interrupt is set whenever there are 12 or less
bytes of data in the FIFO.) The PINT pin can be used for interrupt-driven systems. The host must
respond to the request by writing data to the FIFO. If at this time the FIFO is empty, it can be
completely filled in a single burst, otherwise a minimum of (16-<threshold>) bytes may be written to
the FIFO in a single burst. This process is repeated until the last byte is transferred into the FIFO.
133