The ECP requests programmed I/O transfers
from the host by activating the PINTR pin. The
programmed I/O will empty or fill the FIFO
using the appropriate direction and mode.
the FIFO. If at this time the FIFO is full, it can
be completely emptied in single burst,
otherwise a minimum of (16-<threshold>) bytes
may be read from the FIFO in a single burst.
a
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 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.
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.
Otherwise
it
may
be
filled
with
writeIntrThreshold bytes.
writeIntrThreshold =
(16-<threshold>) free
bytes in FIFO
readIntrThreshold =
(16-<threshold>) data
bytes in FIFO
An interrupt is generated when
is 0
serviceIntr
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.
An interrupt is generated when
and the number of bytes in the FIFO is greater
than or equal to (16-<threshold>). (If the
is 0
serviceIntr
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
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