CD1284 Datasheet, PDF (67/176 Pages) Intel Corporation – IEEE 1284-Compatible Parallel Interface Controller with Two High-Speed Asynchronous Serial Ports

IEEE 1284-Compatible Parallel Interface Controller — CD1284
5.8
5.8.1
5.8.2
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.
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]):
00 Do nothing — function not enabled
01 Change all <CR> characters to <NL>
10 Change all <NL> characters to <CR> <NL>
11 CR characters changed to NL or NL
When both flags are set (‘11’), only one translation occurs – a CR that changed to NL is not
changed to CRNL.
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.
Datasheet
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