CD1865 datasheet(32/150 Pages) INTEL

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CD1865 — Intelligent Eight-Channel Communications Controller

Datasheet

• Data from the host can be given to the Transmitter FIFO, which is now empty.

• A modem signal changes state.

Three separate service request levels are provided to support the following three categories:

5.4.1

Receive Service Requests

The Receive Service Request is unique because it has two subtypes; that is, it is capable of

returning one of the two different vectors during a service request acknowledge cycle. The two

sub-types are — ‘Receive Good Data’ and ‘Receive Exception’. The reason there are two types

within one category of service request is that, while Good Data and Exceptions require different

handling, they are both of equal priority, and need to be serviced in the order they are received. For

example, suppose two good characters are received, then an exception character, and then another

good character is received. There must be a service request for the first 2 bytes of Good Data, then

for the Exception, and then for more Good Data. If Exception Service Request is at a different

level, the exception character is processed either before or after the Good Data, and not in sequence

as it should be. This method also allows the Receive Good Data-handling routine in the host to be

very fast and efficient, since it only has to move ‘N’ bytes to a buffer. All special-case conditions

can be put in a separate handler, where they do not slow down normal data transfers.

Exception characters are characters with errors or that match the defined special characters, line

breaks, and certain time-out conditions.

Data must not be read from the Receive FIFO or the Receive Status FIFO except when the CD1865

is within the context of a Receive Data Service Request.

5.4.1.1

Receive Good Data



A Receive Good Data Service Request is asserted for any of the following three conditions:

1. RxFIFO threshold reached, and the FIFO contains Good Data.

2. RxFIFO threshold not reached, but the FIFO contains Good Data, and the Receive Data Timer

times-out.

3. RxFIFO threshold not reached, but the FIFO contains Good Data, and the newly arrived data

contains an exception condition.

When any of these conditions occur, the modified service request vector indicates to the host that

the service request is for Good Data. The CD1865 continues to add bytes to the FIFO, and it

increments the Count register for each good byte added, and this allows for optimally efficient use

of the FIFO.

It is not necessary to accept any or all of the Good Data that is available when a Good Data

Interrupt is received. If a host buffer is too full to accept 8 bytes, a smaller number (even 0) can be

read, the service request context left, and the host buffer handled first. The CD1865 again generates

another Good Data Service Request when any of the three conditions listed above are met.

Source

Pin Name

Request Match

Receive data

Transmit data

Modem signal change

CD1865 Datasheet(PDF) 32 Page - Intel Corporation

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