SCD1284 datasheet(67/176 Pages) INTEL

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IEEE 1284-Compatible Parallel Interface Controller — CD1284

Datasheet

5.8

Transmit Special Character Processing

The CD1284 also provides some special character handling on the transmit side – embedded

transmit commands and direct commands to transmit predefined special characters. Figure 10 on

page 70 illustrates the process of special character handling.

5.8.1

Line Terminating Characters

On transmit, there are four possible substitutions based on the setting of two flags, the ONLCR and

OCRNL bits (COR5[1:0]):

When both flags are set (‘11’), only one translation occurs – a CR that changed to NL is not

changed to CRNL.

5.8.2

Embedded Transmit Commands

The CD1284 has a special feature that optionally allows specific ‘escape’ character sequences in

the transmit data stream to be interpreted as commands. These are called ETCs (embedded transmit

commands) and are enabled in COR2[5]. These sequences can insert programmed time delays

between characters and generate a line break on the transmit data output.

If enabled, an ETC is detected when the two- or three-character escape sequence is detected in the

transmit FIFO. An escape-character sequence is comprised of the special escape character followed

by the command character and an optional count for the delay period. The escape character is an

all-zero character (null or NUL in the ASCII character set map). Five commands are supported in

the ETC command set:

• NUL NUL

• NUL x’81

• NUL x’82 x’xx

• NUL x’83

• NUL x’01–x’3F

NUL NUL – Send One NUL Character

This command sequence allows the NUL character to be sent alone. Thus, this ‘escapes’ the escape

when it is desired to send a null character.

NUL x’81 – Send BREAK

This sequence forces the transmitter to enter the line-break condition for at least one character time.

Several conditions control the continuation and/or termination of the line break.

Do nothing — function not enabled

Change all <CR> characters to <NL>

Change all <NL> characters to <CR> <NL>

CR characters changed to NL or NL

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