SCD1284 datasheet(62/176 Pages) INTEL

62 / 176 page

CD1284 — IEEE 1284-Compatible Parallel Interface Controller

Datasheet

5.7.1.2

Errored Character Processing

The CD1284 can easily manage received characters with errors (such as, parity, framing, and

overrun). If none of the special processing functions are enabled, errored characters are delivered

to the CPU through a receive exception service request. As defined by the PEH[2:0] bits

(COR4[2:0]), these characters can be handled in one of the following ways:

• Parity errors can be ignored — the character is placed in the FIFO as good data and is given to

the CPU as any other received good data.

• An errored character can be replaced with a NULL (x’00) character in the FIFO.

• An errored character can be replaced in the FIFO with the 3-byte string x’FF–NULL-character.

If this mode is enabled and an actual good x’FF character is received, it is replaced in the FIFO

with the two character sequence x’FF-x’FF.

• An errored character can be discarded.

Received breaks are handled differently from other errored characters. They can be processed,

based on the settings of the IGNBRK and -BRKINT bits (COR4[4:3]), as:

• Reported as an errored character by a received exception service request.

• Replaced with a good NULL (x’00) character in the FIFO.

• Discarded.

5.7.1.3

LNext

LNext (Literal Next) allows ‘escaping’ or ignoring any special meaning of special characters and

considers them as normal data. The escape character is defined by the value in the LNC register. If

the CD1284 receives this character, places it and the next character in the FIFO without further

processing. As an example, this allows a flow-control character to be received without it causing

actual flow-control activity. LNext can be enabled to operate on characters received with errors

(such as, parity, framing, and overrun), otherwise errored characters are handled normally and the

next character is not escaped.

5.7.1.4

ISTRIP

ISTRIP is a simple function that, if enabled, resets the most-significant bit (bit 7) of all received

good characters. If the character has a parity or framing error, the ISTRIP function does nothing

and the character is sent to the CPU as a normal receive exception service request.

000

Do nothing – function not enabled

001

Received NL changed to CR

010

Received CR changed to NL

011

Received CR change to NL; NL changed to CR

100

Received CR discarded

101

Received CR discarded; NL changed to CR

110

Received CR discarded

111

Received CR discarded; NL changed to CR

SCD1284 Datasheet(PDF) 62 Page - Intel Corporation

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