CIRCC datasheet(63/70 Pages) SMSC

63 / 70 page

Receive

Receiving messages with Programmed I/O using

FIFO Interrupt requires reading a fixed number of

data bytes, usually related to the threshold,

whenever the FIFO Interrupt becomes active.

An appropriate FIFO Threshold value allows the

host to efficiently satsify the FIFO service

requests

until

the

message

reception

complete.

IOCHRDY Time-out

In programmed I/O mode when AEN = low and

String Move = active, IOCHRDY can be used to

slightly extend the access cycle if the FIFO is

temporarily unable to fulfill the transfer request

(Figure 33).

If IOCHRDY remains inactive for

more than 10Fs, a time-out error occurs and

subsequent IOCHRDY cycles are prevented until

the string move bit is specifically reactivated.

Because of the 10Fs IOCHRDY time-out, it is

recommended that string move timing only be

used for 1.152 Mbps transfers and above.

DMA Enable

IOW

String Move

Tx Enable

TxServReq

FIFO Int. Enable

FIFO Interrupt

Data Done

EOM Interrupt

FIGURE 31 - INTERRUPT DRIVEN PROGRAMMED I/O TRANSMIT TIMING

DMA Enable

IOR

String Move

Rx Enable

RxServReq

FIFO Int. Enable

FIFO Interrupt

EOM Interrupt

FIGURE 32 - INTERRUPT DRIVEN PROGRAMMED I/O RECEIVE TIMING

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