diff --git a/index.js b/index.js
index efea92e..2649ecd 100644
--- a/index.js
+++ b/index.js
@@ -135,7 +135,7 @@ function _readFC16(data, next) {
  * @private
  */
 function _writeBufferToPort(buffer) {
-    var transaction = this._transactions[this._port.transactionsCounter];
+    var transaction = this._transactions[this._port._transactionIdWrite];
 
     this._port.write(buffer);
     if (transaction) {
@@ -208,17 +208,17 @@ ModbusRTU.prototype.open = function(callback) {
                 callback(error);
 
             /* init ports transaction id and counter */
-            modbus._port._transactionId = 1;
-            modbus._port.transactionsCounter = 1;
+            modbus._port._transactionIdRead = 1;
+            modbus._port._transactionIdWrite = 1;
 
             /* On serial port success
              * register the modbus parser functions
              */
             modbus._port.on("data", function(data) {
                 // set locale helpers variables
-                var transaction = modbus._transactions[modbus._port._transactionId];
+                var transaction = modbus._transactions[modbus._port._transactionIdRead];
 
-                // the _transactionId can be missing, ignore wrong transaction it's
+                // the _transactionIdRead can be missing, ignore wrong transaction it's
                 if (!transaction) {
                     return;
                 }
@@ -381,7 +381,7 @@ ModbusRTU.prototype.writeFC2 = function(address, dataAddress, length, next, code
     code = code || 2;
 
     // set state variables
-    this._transactions[this._port.transactionsCounter] = {
+    this._transactions[this._port._transactionIdWrite] = {
         nextAddress: address,
         nextCode: code,
         nextLength: 3 + parseInt((length - 1) / 8 + 1) + 2,
@@ -434,7 +434,7 @@ ModbusRTU.prototype.writeFC4 = function(address, dataAddress, length, next, code
     code = code || 4;
 
     // set state variables
-    this._transactions[this._port.transactionsCounter] = {
+    this._transactions[this._port._transactionIdWrite] = {
         nextAddress: address,
         nextCode: code,
         nextLength: 3 + 2 * length + 2,
@@ -474,7 +474,7 @@ ModbusRTU.prototype.writeFC5 = function(address, dataAddress, state, next) {
     var code = 5;
 
     // set state variables
-    this._transactions[this._port.transactionsCounter] = {
+    this._transactions[this._port._transactionIdWrite] = {
         nextAddress: address,
         nextCode: code,
         nextLength: 8,
@@ -519,7 +519,7 @@ ModbusRTU.prototype.writeFC6 = function(address, dataAddress, value, next) {
     var code = 6;
 
     // set state variables
-    this._transactions[this._port.transactionsCounter] = {
+    this._transactions[this._port._transactionIdWrite] = {
         nextAddress: address,
         nextCode: code,
         nextLength: 8,
@@ -561,7 +561,7 @@ ModbusRTU.prototype.writeFC15 = function(address, dataAddress, array, next) {
     var i = 0;
 
     // set state variables
-    this._transactions[this._port.transactionsCounter] = {
+    this._transactions[this._port._transactionIdWrite] = {
         nextAddress: address,
         nextCode: code,
         nextLength: 8,
@@ -616,7 +616,7 @@ ModbusRTU.prototype.writeFC16 = function(address, dataAddress, array, next) {
     var code = 16;
 
     // set state variables
-    this._transactions[this._port.transactionsCounter] = {
+    this._transactions[this._port._transactionIdWrite] = {
         nextAddress: address,
         nextCode: code,
         nextLength: 8,
diff --git a/ports/tcpport.js b/ports/tcpport.js
index 958c259..18b84fe 100644
--- a/ports/tcpport.js
+++ b/ports/tcpport.js
@@ -22,7 +22,7 @@ var TcpPort = function(ip, options) {
     this.ip = ip;
     this.openFlag = false;
     this.callback = null;
-    this.transactionsCounter = 1;
+    this._transactionIdWrite = 1;
 
     // options
     if (typeof(options) === "undefined") options = {};
@@ -53,7 +53,7 @@ var TcpPort = function(ip, options) {
         buffer.writeUInt16LE(crc, buffer.length - CRC_LENGTH);
 
         // update transaction id
-        modbus._transactionId = data.readUInt16BE(0);
+        modbus._transactionIdRead = data.readUInt16BE(0);
 
         modbusSerialDebug({ action: "receive tcp port", data: data, buffer: buffer });
         modbusSerialDebug(JSON.stringify({ action: "receive tcp port strings", data: data, buffer: buffer }));
@@ -118,13 +118,13 @@ TcpPort.prototype.write = function(data) {
 
     // remove crc and add mbap
     var buffer = new Buffer(data.length + MIN_MBAP_LENGTH - CRC_LENGTH);
-    buffer.writeUInt16BE(this.transactionsCounter, 0);
+    buffer.writeUInt16BE(this._transactionIdWrite, 0);
     buffer.writeUInt16BE(0, 2);
     buffer.writeUInt16BE(data.length - CRC_LENGTH, 4);
     data.copy(buffer, MIN_MBAP_LENGTH);
 
     // set next transaction id
-    this.transactionsCounter = (this.transactionsCounter + 1) % MAX_TRANSACTIONS;
+    this._transactionIdWrite = (this._transactionIdWrite + 1) % MAX_TRANSACTIONS;
 
     // send buffer to slave
     this._client.write(buffer);
diff --git a/ports/tcprtubufferedport.js b/ports/tcprtubufferedport.js
index 60d1ee6..878879f 100644
--- a/ports/tcprtubufferedport.js
+++ b/ports/tcprtubufferedport.js
@@ -28,6 +28,7 @@ var TcpRTUBufferedPort = function(ip, options) {
     this.ip = ip;
     this.openFlag = false;
     this.callback = null;
+    this._transactionIdWrite = 1;
 
     // options
     if (typeof(options) === "undefined") options = {};
@@ -128,7 +129,7 @@ TcpRTUBufferedPort.prototype._emitData = function(start, length) {
     this._buffer = this._buffer.slice(start + length);
 
     // update transaction id
-    this._transactionId = data.readUInt16BE(0);
+    this._transactionIdRead = data.readUInt16BE(0);
 
     if (data.length > 0) {
         var buffer = Buffer.alloc(data.length + CRC_LENGTH);
@@ -211,16 +212,16 @@ TcpRTUBufferedPort.prototype.write = function(data) {
             break;
     }
 
-    // get next transaction id
-    var transactionsId = (this._transactionId + 1) % MAX_TRANSACTIONS;
-
     // remove crc and add mbap
     var buffer = new Buffer(data.length + MIN_MBAP_LENGTH - CRC_LENGTH);
-    buffer.writeUInt16BE(transactionsId, 0);
+    buffer.writeUInt16BE(this._transactionIdWrite, 0);
     buffer.writeUInt16BE(0, 2);
     buffer.writeUInt16BE(data.length - CRC_LENGTH, 4);
     data.copy(buffer, MIN_MBAP_LENGTH);
 
+    // get next transaction id
+    this._transactionIdWrite = (this._transactionIdWrite + 1) % MAX_TRANSACTIONS;
+
     // send buffer to slave
     this._client.write(buffer);
 
diff --git a/test/ports/tcpportrtubuffered.test.js b/test/ports/tcpportrtubuffered.test.js
index d9101c1..8ca65f7 100644
--- a/test/ports/tcpportrtubuffered.test.js
+++ b/test/ports/tcpportrtubuffered.test.js
@@ -172,7 +172,7 @@ describe("Modbus TCP RTU buffered port", function() {
     describe("#write", function() {
         it("should write a valid TCP RTU message to the port", function() {
             port.write(new Buffer("0103000500045408", "hex"));
-            expect(port._client._data.toString("hex")).to.equal("000400000006010300050004");
+            expect(port._client._data.toString("hex")).to.equal("000700000006010300050004");
         });
     });
 });