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Old 04-07-2004, 10:40 AM   #1
LQ Newbie
Registered: Apr 2004
Posts: 15

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Serial Port Issues

For some reason the serial port on this laptop seems inactive:

NEC Versa V/75
486 DX4 75Mhz
20 Mb RAM
540 Mb Harddrive

Slackware 9.1 (but this has happened with other distros as well)

When I try to use minicom (The linux equivelent of hyperterminal) The device is shown as "offline" and I can't seem to send or receive data via the serial port. I've checked the IRQ and Address in the BIOS and they match what they should be so I am at a loss. I know the serial port works because I have a second hard drive for this laptop that has Win98 and it communicates just fine in hyperterminal. Here is the relative info from dmesg, stty, setserial and minicom:

root@xxxxxxxx:~# dmesg | grep tty
ttyS00 at 0x03f8 (irq = 4) is a 16450

root@xxxxxxxx:~# setserial -a /dev/ttyS0
/dev/ttyS0, Line 0, UART: 16450, Port: 0x03f8, IRQ: 4
Baud_base: 115200, close_delay: 50, divisor: 0
closing_wait: 3000
Flags: spd_normal skip_test

root@xxxxxxxx:~# stty -F /dev/ttyS0 -a
speed 9600 baud; rows 0; columns 0; line = 0;
intr = ^C; quit = ^\; erase = ^?; kill = ^U; eof = ^D; eol = <undef>;
eol2 = <undef>; start = ^Q; stop = ^S; susp = ^Z; rprnt = ^R; werase = ^W;
lnext = ^V; flush = ^O; min = 1; time = 0;
-parenb -parodd cs8 hupcl -cstopb cread clocal -crtscts
-ignbrk -brkint -ignpar -parmrk -inpck -istrip -inlcr -igncr icrnl ixon -ixoff
-iuclc -ixany -imaxbel
opost -olcuc -ocrnl onlcr -onocr -onlret -ofill -ofdel nl0 cr0 tab0 bs0 vt0 ff0
isig icanon iexten echo echoe echok -echonl -noflsh -xcase -tostop -echoprt
echoctl echoke

Minicom settings

┌───────────────────────────────────────────────── ──────────────────────┐
Ю A - Serial Device : /dev/ttyS0 Ю
Ю B - Lockfile Location : /var/lock Ю
Ю C - Callin Program : Ю
Ю D - Callout Program : Ю
Ю E - Bps/Par/Bits : 9600 8N1 Ю
Ю F - Hardware Flow Control : Yes Ю
Ю G - Software Flow Control : No Ю
Ю Change which setting? Ю
└───────────────────────────────────────────────── ──────────────────────┘

CTRL-A Z for help | 9600 8N1 | NOR | Minicom 2.00.0 | VT102 | Offline

I would like to at least be able to use minicom for serial communications. Any help would be much appreciated.

Old 04-08-2004, 09:29 AM   #2
LQ Newbie
Registered: Apr 2004
Posts: 15

Original Poster
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Okay, I figured it out and I'll post how I got it to work in case any other poor sap like myself runs into the same issues. There are a few things (at least in slackware) that need to be done in order for the serial port to be enabled and properly configured.

1. be sure that the /etc/rc.d/rc.S file contains a reference to start the rc.serial script and that it is UNCOMMENTED.

2. configure the /etc/serial.conf file accordingly as (at least in this install) all settings are commented out.

3. Make sure that the settings are appropriate for your serial port. I went around and around and found out that my serial port uses a uart of 16550A rather than the "detected" 16450. Be careful with this file as if not properly configured, your machine could lock up at bootup. It didn't happen to me, but from what I've read in the docs, it supposedly can happen.

4. Do an efficient test. If connecting to a win machine be sure that hyperterminal is up and running first before running minicom otherwise minicom will just come up as "offline" and you will think that your problem has not been solved.

These steps are how I was able to finally get my serial port up and communicating.


Last edited by corster; 04-08-2004 at 09:32 AM.


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