Read Non Printable characters from serial port

caduser1 · 03-16-2009, 01:56 PM

Can someone please shed some light on the following issue. I am trying to write a shell script to read and send data over a serial port. I could successfully send and receive data, but I need to find a way to detect when an ACK or ENQ or NAK (non-printable characters) has been sent by the device at the end the serial connection.

Any help is appreciated.

David1357 · 03-16-2009, 04:23 PM

Quote:

Originally Posted by caduser1

Any help is appreciated.

Have you tried using "read" with "-r -s -n 1"? That should let you read one character at a time. You can create variables with the special characters using printf:

Code:

# Create variables for the special characters
ACK=$(printf "\x6")
ENQ=$(printf "\x5")
NAK=$(printf "\x19")
# Open /dev/ttyS0 for reading and writing as file descriptor 5
5<>/dev/ttyS0
while true ;
do
    # Read one character from file descriptor 5
    read -u 5 -r -s -n 1 CHAR
    case $CHAR in
        $ACK)
            # Handle an ACK
        $ENQ)
            # Handle an ENQ
        $NAK)
            # Handle an NAK
        *)
            # Handle other characters
    esac
    ;;
done

I hope you are using bash, and I wish I had an easy way of testing this.

damien_d · 03-17-2009, 11:22 PM

Quote:

Originally Posted by caduser1

Can someone please shed some light on the following issue. I am trying to write a shell script to read and send data over a serial port. I could successfully send and receive data, but I need to find a way to detect when an ACK or ENQ or NAK (non-printable characters) has been sent by the device at the end the serial connection.

Is the serial port in raw mode? i.e. ?

Code:

stty -F /dev/ttyS0 115200 raw

caduser1 · 03-18-2009, 08:47 PM

Quote:

Originally Posted by David1357

Have you tried using "read" with "-r -s -n 1"? That should let you read one character at a time. You can create variables with the special characters using printf:

Code:

# Create variables for the special characters
ACK=$(printf "\x6")
ENQ=$(printf "\x5")
NAK=$(printf "\x19")
# Open /dev/ttyS0 for reading and writing as file descriptor 5
5<>/dev/ttyS0
while true ;
do
    # Read one character from file descriptor 5
    read -u 5 -r -s -n 1 CHAR
    case $CHAR in
        $ACK)
            # Handle an ACK
        $ENQ)
            # Handle an ENQ
        $NAK)
            # Handle an NAK
        *)
            # Handle other characters
    esac
    ;;
done

I hope you are using bash, and I wish I had an easy way of testing this.

Thanks. I am using bash. In my system if I tried to set the file descriptor to any value higher than 3, the read statement returns an invalid file descriptor error. With values of 1,2, or 3, it doesn't read from the port. But if I use read -r -s -n 1 CHAR < /dev/ttyS0 I could read from the port, but still cannot detect the non-printable charater.

Thanks

David1357 · 03-19-2009, 01:55 PM

Quote:

Originally Posted by caduser1

TBut if I use read -r -s -n 1 CHAR < /dev/ttyS0 I could read from the port, but still cannot detect the non-printable charater.

You may need to combine that with the "raw" mode mentioned by damien_d

caduser1 · 03-19-2009, 02:14 PM

Quote:

Originally Posted by David1357

You may need to combine that with the "raw" mode mentioned by damien_d

Here's my code. Please feel free to comment.

#!/bin/bash

#Port Initialization
stty -F /dev/ttyS000 ispeed 9600 ospeed 9600 sane cs8 -parodd -cstopb ixon

#Port Variable Definition
PORT="/dev/ttyS000"

#Control Characters Definition
STX=$(printf "\x02")
ETX=$(printf "\x03")
ENQ=$(printf "\x05")
ACK=$(printf "\x06")
NACK=$(printf "\x15")

LINETEST=$STX"AREYUTHERE"$ETX

#Some Timers
ENQTIMER=2
PMSTIMER=5
AREYUTHERETIMER=5

RESP="GRS"
RESP2="CHK"

SUCCESS=1
FAILURE=0

DATAFILE="/usr/bin/dgrp/pmsdata.txt"
LOGFILE="/usr/bin/dgrp/log.txt"

Init ()
{
echo -en $ENQ > $PORT
read -r -s -t $ENQTIMER -n 1 DATA1 < $PORT

case $DATA1 in
$ACK)
echo -en $LINETEST > $PORT
read -r -s -t $ENQTIMER -n 1 DATA2 < $PORT
case $DATA2 in
$ACK)
RCODE=$SUCCESS
;;
*)
RCODE=$FAILURE
;;
esac
;;

$ENQ)
echo -en $ACK > $PORT
read -r -s -t $ENQTIMER DATA3 < $PORT

case $DATA3 in
AREYUTHERE)
echo -en $ACK > $PORT
RCODE=$SUCCESS
;;
*)
echo -en $NACK > $PORT
RCODE=$FAILURE
;;
esac
;;

*)
RCODE=$FAILURE
;;

esac
}

NormalOp ()
{
while true
do
read -u 1 -r -s -t $PMSTIMER -n 1 DATA3

case $DATA3 in
$ENQ)
echo -en $ACK > $PORT
read -u 1 -r -s -t $PMSTIMER DATA4
LEN=${#DATA4[*]}

STARTOFDATA=${DATE4:0:3}
ENDOFDATA=${DATA4:-3}
MESSAGE=${DATA4:1:3}

if [ "$STARTOFDATA" = "STX" -a "$ENDOFDATA" = "ETX" ]; then

if [ "$MESSAGE" = "CHK" -o "$MESSAGE" = "EDT" -o "$MESSAGE" = "RST" -o "$MESSAGE" = "STS" -o "$MESSAGE" = "MW " ]; then
echo -e $ACK > $PORT
echo $DATA4 >> $DATAFILE
echo $DATA4 >> $LOGFILE
elif
[ "${MESSAGE:1:10}" = "AREYUTHERE" -o "${MESSAGE:1:8}" = "LINETEST" -o "${MESSAGE:1:3}" = "GRS" -o "${MESSAGE:1:5}" = "RQINZ" ]; then
echo -e $ACK > $PORT
else
echo -e $NACK > $PORT
echo $DATA >> $LOGFILE
fi
else
echo -en $NACK > $PORT
fi
;;
esac
done
}
while true
do
Init

if [ "$RCODE" -eq 1 ]; then
echo "Link success..."
break
else
echo "Link not initialized..."
sleep 2
fi

done

NormalOp

exit 0

caduser1 · 03-19-2009, 02:18 PM

Quote:

Originally Posted by caduser1

Here's my code. Please feel free to comment.

#!/bin/bash

#Port Initialization
stty -F /dev/ttyS000 ispeed 9600 ospeed 9600 sane cs8 -parodd -cstopb ixon

#Port Variable Definition
PORT="/dev/ttyS000"

#Control Characters Definition
STX=$(printf "\x02")
ETX=$(printf "\x03")
ENQ=$(printf "\x05")
ACK=$(printf "\x06")
NACK=$(printf "\x15")

LINETEST=$STX"AREYUTHERE"$ETX

#Some Timers
ENQTIMER=2
PMSTIMER=5
AREYUTHERETIMER=5

RESP="GRS"
RESP2="CHK"

SUCCESS=1
FAILURE=0

DATAFILE="/usr/bin/dgrp/pmsdata.txt"
LOGFILE="/usr/bin/dgrp/log.txt"

Init ()
{
echo -en $ENQ > $PORT
read -r -s -t $ENQTIMER -n 1 DATA1 < $PORT

case $DATA1 in
$ACK)
echo -en $LINETEST > $PORT
read -r -s -t $ENQTIMER -n 1 DATA2 < $PORT
case $DATA2 in
$ACK)
RCODE=$SUCCESS
;;
*)
RCODE=$FAILURE
;;
esac
;;

$ENQ)
echo -en $ACK > $PORT
read -r -s -t $ENQTIMER DATA3 < $PORT

case $DATA3 in
AREYUTHERE)
echo -en $ACK > $PORT
RCODE=$SUCCESS
;;
*)
echo -en $NACK > $PORT
RCODE=$FAILURE
;;
esac
;;

*)
RCODE=$FAILURE
;;

esac
}

NormalOp ()
{
while true
do
read -u 1 -r -s -t $PMSTIMER -n 1 DATA3

case $DATA3 in
$ENQ)
echo -en $ACK > $PORT
read -u 1 -r -s -t $PMSTIMER DATA4
LEN=${#DATA4[*]}

STARTOFDATA=${DATE4:0:3}
ENDOFDATA=${DATA4:-3}
MESSAGE=${DATA4:1:3}

if [ "$STARTOFDATA" = "STX" -a "$ENDOFDATA" = "ETX" ]; then

if [ "$MESSAGE" = "CHK" -o "$MESSAGE" = "EDT" -o "$MESSAGE" = "RST" -o "$MESSAGE" = "STS" -o "$MESSAGE" = "MW " ]; then
echo -e $ACK > $PORT
echo $DATA4 >> $DATAFILE
echo $DATA4 >> $LOGFILE
elif
[ "${MESSAGE:1:10}" = "AREYUTHERE" -o "${MESSAGE:1:8}" = "LINETEST" -o "${MESSAGE:1:3}" = "GRS" -o "${MESSAGE:1:5}" = "RQINZ" ]; then
echo -e $ACK > $PORT
else
echo -e $NACK > $PORT
echo $DATA >> $LOGFILE
fi
else
echo -en $NACK > $PORT
fi
;;
esac
done
}
while true
do
Init

if [ "$RCODE" -eq 1 ]; then
echo "Link success..."
break
else
echo "Link not initialized..."
sleep 2
fi

done

NormalOp

exit 0

Here's the log of what happens when I execute it:
2004.12.7: 15:17:24 - Sending ENQ
2004.12.7: 15:17:25 - Received: {ACK}
2004.12.7: 15:17:25 - VMs_Xmit->Sending: {STX}AREYUTHERE{ETX}
2004.12.7: 15:17:29 - Received: {NAK}
2004.12.7: 15:17:29 - Received NAK - Sending again
2004.12.7: 15:17:29 - Sending ENQ
2004.12.7: 15:17:35 - Timed Out - Trying again
2004.12.7: 15:17:35 - Sending ENQ
2004.12.7: 15:17:35 - Received: {ACK}
2004.12.7: 15:17:35 - VMs_Xmit->Sending: {STX}AREYUTHERE{ETX}
2004.12.7: 15:17:39 - Received: {NAK}
2004.12.7: 15:17:39 - Received NAK - Sending again
2004.12.7: 15:17:39 - Sending ENQ
2004.12.7: 15:17:45 - Timed Out - Trying again
2004.12.7: 15:17:45 - Sending ENQ
2004.12.7: 15:17:45 - Received: {ACK}
2004.12.7: 15:17:46 - VMs_Xmit->Sending: {STX}AREYUTHERE{ETX}
2004.12.7: 15:17:49 - Received: {NAK}
2004.12.7: 15:17:49 - Received NAK - Sending again
2004.12.7: 15:17:55 - Received: {ACK}