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CHAPTER 3 FUNCTIONAL DESCRIPTION
User’s Manual S14054EJ4V0UM
45
(b) SKIP signal
The port number of the receive FIFO whose data is read through the FIFO bus is instructed by the
µ
PD98431. By inputting the SKIP signal when the RXFA signal goes high after reading the receive FIFO has
been enabled or while receive data is being read by means of burst transfer, the host system can read being
a port other than the one specified by the
µ
PD98431.
As described above, the sequence in which receive data is transferred is predetermined, and the SKIP signal
is used to forcibly change the port from which receive data is to be read next, under the instruction of the
host system.
When the SKIP signal is input, the
µ
PD98431 stops reading the receive data from the current port, outputs
0000B to the RXFDQ or FDQ pin, and enters idle status. The RXFA signal goes low once. Next, it outputs
the port number of the next port that is ready for transferring receive data to the RXFPT and makes the
RXFA signal high again. If the PASS signal is input from the host system at this time, data is read from the
next port.
The data of the port that is skipped by the SKIP signal is retained. If reading the receive data of the other
port has been completed or if the original port is selected by input of the new SKIP signal, the port that was
skipped waits for input of a new PASS signal, and then starts transferring the rest of the receive data.
Figure 3-9 shows an example of selecting a port using the SKIP signal before starting to read data. In this
case, a port is selected two clocks of FCLK after the SKIP signal has been detected.
Do not input the SKIP signal for the duration of two or more clocks. To skip two or more ports in a row by
inputting the SKIP signal two times or more, input the next SKIP signal after confirming that the new port has
been selected after inputting the first SKIP signal for the duration of one clock.