367 lines
6.9 KiB
HTML
367 lines
6.9 KiB
HTML
<HTML
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><HEAD
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>Serial printers under lpd</TITLE
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CLASS="sect1"
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><H1
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CLASS="sect1"
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><A
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NAME="serial"
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></A
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>Serial printers under lpd</H1
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><A
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NAME="AEN2234"
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></A
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><P
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>Serial printers are rather tricky under lpd.</P
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><DIV
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CLASS="sect2"
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><H2
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CLASS="sect2"
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><A
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NAME="serial-printcap"
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></A
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>Setting up in printcap</H2
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><P
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>Lpd provides five attributes which you can set in<SPAN
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CLASS="emphasis"
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><I
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CLASS="emphasis"
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>/etc/printcap</I
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></SPAN
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> to control all the settings of
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the serial port a printer is on. Read the <SPAN
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CLASS="emphasis"
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><I
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CLASS="emphasis"
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><A
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HREF="http://www.linuxprinting.org/man/printcap.5.html"
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TARGET="_top"
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>printcap</A
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></I
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></SPAN
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> man page and note the meanings of<SPAN
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CLASS="emphasis"
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><I
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CLASS="emphasis"
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>br#</I
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></SPAN
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>, <SPAN
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CLASS="emphasis"
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><I
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CLASS="emphasis"
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>fc#</I
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></SPAN
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>,<SPAN
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CLASS="emphasis"
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><I
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CLASS="emphasis"
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>xc#</I
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></SPAN
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>, <SPAN
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CLASS="emphasis"
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><I
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CLASS="emphasis"
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>fs#</I
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></SPAN
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> and<SPAN
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CLASS="emphasis"
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><I
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CLASS="emphasis"
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>xs#</I
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></SPAN
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>. The last four of these attributes
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are bitmaps indicating the settings for use the port. The<SPAN
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CLASS="emphasis"
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><I
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CLASS="emphasis"
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>br#</I
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></SPAN
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> attribute is simply the baud rate, eg
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`<TT
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CLASS="literal"
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>br#9600</TT
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>'.</P
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><P
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>It is very easy to translate from <A
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HREF="http://www.linuxprinting.org/man/stty.1.html"
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TARGET="_top"
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>stty</A
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> settings to printcap flag settings. If you need to,
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see the man page for stty now.</P
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><P
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>Use stty to set up the printer port so that you can cat a file to
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it and have it print correctly. Here's what `<SPAN
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CLASS="emphasis"
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><I
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CLASS="emphasis"
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>stty
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-a</I
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></SPAN
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>' looks like for my printer port:<PRE
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CLASS="screen"
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> dina:/usr/users/andy/work/lpd/lpd# stty -a < /dev/ttyS2
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speed 9600 baud; rows 0; columns 0; line = 0;
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intr = ^C; quit = ^\; erase = ^?; kill = ^U; eof = ^D; eol = <undef>;
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eol2 = <undef>; start = ^Q; stop = ^S; susp = ^Z; rprnt = ^R; werase = ^W;
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lnext = ^V; min = 1; time = 0;
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-parenb -parodd cs8 hupcl -cstopb cread -clocal -crtscts
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-ignbrk -brkint -ignpar -parmrk -inpck -istrip -inlcr
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-igncr -icrnl ixon -ixoff -iuclc -ixany -imaxbel
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-opost -olcuc -ocrnl -onlcr -onocr -onlret -ofill -ofdel nl0 cr0 tab0
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bs0 vt0 ff0
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-isig -icanon -iexten -echo -echoe -echok -echonl -noflsh -xcase
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-tostop -echoprt -echoctl -echoke</PRE
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>
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The only changes between this and the way the port is initialized
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at bootup are <TT
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CLASS="literal"
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>-clocal</TT
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>, <TT
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CLASS="literal"
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>-crtscts</TT
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>, and <TT
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CLASS="literal"
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>ixon</TT
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>. Your port may well be different
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depending on how your printer does flow control.</P
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><P
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>You actually use stty in a somewhat odd way. Since stty operates
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on the terminal connected to it's standard input, you use it to
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manipulate a given serial port by using the `<TT
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CLASS="literal"
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><</TT
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>' character as above.</P
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><P
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>Once you have your stty settings right, so that `<SPAN
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CLASS="emphasis"
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><I
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CLASS="emphasis"
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>cat
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file > /dev/ttyS2</I
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></SPAN
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>' (in my case) sends the file to
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the printer, look at the file
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/usr/src/linux/include/asm-i386/termbits.h. This contains a lot of
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#defines and a few structs (You may wish to cat this file to
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the printer (you do have that working, right?) and use it as
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scratch paper). Go to the section that starts out</P
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><P
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> <PRE
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CLASS="screen"
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>/* c_cflag bit meaning */
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#define CBAUD 0000017</PRE
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>This section lists the meaning of the <SPAN
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CLASS="emphasis"
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><I
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CLASS="emphasis"
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>fc#</I
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></SPAN
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>
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and <SPAN
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CLASS="emphasis"
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><I
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CLASS="emphasis"
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>fs#</I
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></SPAN
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> bits. You will notice that the
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names there (after the baud rates) match up with one of the lines
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of stty output. Didn't I say this was going to be easy?</P
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><P
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>Note which of those settings are preceded with a - in your stty
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output. Sum up all those numbers (they are octal). This represents
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the bits you want to clear, so the result is your<SPAN
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CLASS="emphasis"
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><I
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CLASS="emphasis"
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>fc#</I
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></SPAN
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> capability. Of course, remember that
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you will be setting bits directly after you clear, so you can just
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use `<TT
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CLASS="literal"
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>fc#0177777</TT
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>' (I do).</P
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><P
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>Now do the same for those settings (listed in this section) which
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do not have a - before them in your stty output. In my example the
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important ones are CS8 (0000060), HUPCL (0002000), and CREAD
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(0000200). Also note the flags for your baud rate (mine is
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0000015). Add those all up, and in my example you get
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0002275. This goes in your <SPAN
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CLASS="emphasis"
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><I
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CLASS="emphasis"
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>fs#</I
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></SPAN
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> capability
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(`<TT
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CLASS="literal"
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>fs#02275</TT
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>' works fine in my
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example).</P
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><P
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>Do the same with set and clear for the next section of the include
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file, "c_lflag bits". In my case I didn't have to set
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anything, so I just use `<TT
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CLASS="literal"
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>xc#0157777</TT
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>' and `<TT
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CLASS="literal"
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>xs#0</TT
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>'.</P
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></DIV
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><DIV
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CLASS="sect2"
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><H2
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CLASS="sect2"
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><A
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NAME="AEN2276"
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></A
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>Older serial printers that drop characters</H2
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><P
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>Jon Luckey points out that some older serial printers with
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ten-cent serial interfaces and small buffers<SPAN
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CLASS="emphasis"
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><I
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CLASS="emphasis"
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>really</I
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></SPAN
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> mean stop when they say so with flow
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control. He found that disabling the FIFO in his Linux box's
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16550 serial port with <TT
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CLASS="literal"
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><A
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HREF="http://www.linuxprinting.org/man/setserial.8.html"
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TARGET="_top"
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>setserial</A
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></TT
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> corrected the problem of dropped
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characters (you apparently just specify the UART type as an 8250
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to do this).</P
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