Digi NS9750 - Manual (Page 695)

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Note:
Traffic direction in the IEEE 1284 is classified as either forward or reverse.
The forward direction is equivalent to NS9750 receive. Similarly, the
reverse direction is equivalent to NS9750 transmit.
Compatibility mode
Compatibility mode is the standard parallel port (SPP) forward transmission mode
(from the host), also known as the Centronics mode. The incoming data is routed into
the
FORWARD DATA IN FIFO
, an acknowledge signal is generated by the 1284 peripheral,
and DMA requests are issued to the BBus until the
FORWARD DATA IN FIFO
is empty.
Figure 96 shows the timing relationship on the port interface.
Figure 96: Compatibility mode data transfer cycle