CD1284 Datasheet, PDF (62/176 Pages) Intel Corporation – IEEE 1284-Compatible Parallel Interface Controller with Two High-Speed Asynchronous Serial Ports

CD1284 — IEEE 1284-Compatible Parallel Interface Controller
5.7.1.2
5.7.1.3
5.7.1.4
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
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.
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.
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.
62
Datasheet