diff --git a/README b/README
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+Tests a serial port and cabling using
+  a) one serial port transmitting data
+  b) another serial port receiving and displaying the data
+
+Usage - Transmitter
+  node serialport_test -p /dev/serial -baud 9600 -t
+
+Usage - Receiver 
+  node serialport_test -p /dev/serial -baud 9600 -r
+
+
+Other command line arguments
+
+  -h       help
+  -l       get list of serial ports on the computer
+  --baud   set baud rate
+
diff --git a/serialport_test.js b/serialport_test.js
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+/*
+ * Serialport Test - Transmitter and Receiver
+ * In Transmitter Mode this program opens a serial port and writes
+ * lots of data to a serial port
+ * In Receiver Mode this program receives the data and displays it on the
+ * console
+
+ * (c) Copyright 2017 Roger Hardiman
+ */
+
+// External Dependencies
+var SerialPort = require('serialport');
+var args = require('commander');
+
+// Command line arguments
+args.description('Serialport Test Transmitter/Receiver');
+args.option('-l, --list','List serial ports');
+args.option('-p, --port <name>','Serial Port eg COM1 or /dev/ttyUSB0');
+args.option('-b, --baud <value>','Baud Rate. Default 2400',parseInt);
+args.option('--parity <value>','Parity none, even, odd. Default none');
+args.option('-t, --transmitter','Transmitter');
+args.option('-r, --receiver','Receiver');
+args.parse(process.argv);
+
+// Initial message
+console.log('');
+console.log('Serialport Test Transmitter');
+console.log('(c) Roger Hardiman 2017 www.rjh.org.uk');
+console.log('Use -h for help');
+console.log('');
+
+// List available serial ports
+if (args.list || (!args.port)) {
+  if (!args.list) {
+    console.log('ERROR: No serial port name specified');
+  }
+  console.log('Available serial ports are:-');
+  SerialPort.list(function(err,ports) {
+    if (err) {
+      console.log(err);
+      return;
+    }
+    ports.forEach(function(port) {
+      console.log(port.comName + '\t' + (port.pnpId || '') + '\t' + (port.manufacturer || ''));
+    });
+    console.log('');
+  });
+  return;
+}
+
+// Must be a transmitter or a receiver
+if (!args.transmitter && !args.receiver) {
+  console.log('ERROR: Must use -transmitter OR -receiver (-t OR -r)');
+  console.log('');
+  return;
+}
+
+
+
+// Defaults 9600 8-N-1
+var serial_port = '';
+var baud_rate = 9600;
+var data_bits = 8;
+var parity = 'none';
+var stop_bits = 1;
+
+// User Settings
+if (args.port) serial_port = args.port;
+if (args.baud) baud_rate = args.baud;
+if (args.parity === 'none' || args.parity === 'odd' || args.parity === 'even') parity = args.parity;
+
+// Open Serial Port.
+var port = new SerialPort(serial_port, {
+    baudrate: baud_rate,
+    parity: parity,
+    dataBits: data_bits,
+    stopBits: stop_bits,
+});
+
+
+// Callback - Error 
+port.on('error', function(err) {
+    console.log(err);
+    console.log('');
+    process.exit(1);
+});
+
+// Callback - Open
+var stream = port.on('open', function(err) {
+    if (err) {
+        console.log('Serial Port Error : ' + err);
+    } else {
+        console.log('Serial Port ' + serial_port + ' open ' + baud_rate + '-' + parity + '-' + stop_bits);
+
+        if (args.transmitter) {
+          console.log('Transmitting');
+          setImmediate(send_message);
+        } 
+    }
+});
+
+var counter = 0;
+function send_message() {
+  counter++;
+  writeAndDrain(counter + ' ' + 'the quick brown fox jumps over the lazy dog\r\n',function () {
+    setTimeout(send_message,300); // call the send message again in 300ms
+  });
+}
+
+function writeAndDrain (data, callback) {
+  stream.write(data, function () {
+    stream.drain(callback);
+  });
+}
+
+// Callback - Data
+port.on('data', function(buffer) {
+
+    // write to console
+    for (var i = 0; i < buffer.length; i++) {
+      var next_byte = buffer[i];
+      if (next_byte >= 32 && next_byte <=126) {
+        process.stdout.write(String.fromCharCode(next_byte));
+      } else if (next_byte == 10 ) {
+        process.stdout.write('\n');
+      } else {
+        process.stdout.write('['+DecToHexPad(next_byte,2)+']');
+      }
+    }
+});
+
+// Callback - Disconnected (eg USB removal) 
+port.on('disconnect', function(err) {
+    console.log('Disconnected ' + err);
+    process.exit(1);
+});
+
+function DecToHexPad(decimal,size) {
+    var ret_string = decimal.toString('16').toUpperCase();
+    while (ret_string.length < size) {
+        ret_string = '0' + ret_string;
+    }
+    return ret_string;
+}
+