diff --git a/build-serialConnectionManager-Desktop_Qt_5_13_1_GCC_64bit-Debug/mainwindow.o b/build-serialConnectionManager-Desktop_Qt_5_13_1_GCC_64bit-Debug/mainwindow.o
index 0dd8272..b2310df 100644
Binary files a/build-serialConnectionManager-Desktop_Qt_5_13_1_GCC_64bit-Debug/mainwindow.o and b/build-serialConnectionManager-Desktop_Qt_5_13_1_GCC_64bit-Debug/mainwindow.o differ
diff --git a/build-serialConnectionManager-Desktop_Qt_5_13_1_GCC_64bit-Debug/modbusmaster.o b/build-serialConnectionManager-Desktop_Qt_5_13_1_GCC_64bit-Debug/modbusmaster.o
index 20017e6..856a53e 100644
Binary files a/build-serialConnectionManager-Desktop_Qt_5_13_1_GCC_64bit-Debug/modbusmaster.o and b/build-serialConnectionManager-Desktop_Qt_5_13_1_GCC_64bit-Debug/modbusmaster.o differ
diff --git a/build-serialConnectionManager-Desktop_Qt_5_13_1_GCC_64bit-Debug/serialConnectionManager b/build-serialConnectionManager-Desktop_Qt_5_13_1_GCC_64bit-Debug/serialConnectionManager
index 8c6bc9c..4398f10 100755
Binary files a/build-serialConnectionManager-Desktop_Qt_5_13_1_GCC_64bit-Debug/serialConnectionManager and b/build-serialConnectionManager-Desktop_Qt_5_13_1_GCC_64bit-Debug/serialConnectionManager differ
diff --git a/serialConnectionManager/mainwindow.cpp b/serialConnectionManager/mainwindow.cpp
index 1c80e36..551a3c1 100644
--- a/serialConnectionManager/mainwindow.cpp
+++ b/serialConnectionManager/mainwindow.cpp
@@ -50,19 +50,23 @@ void MainWindow::printDataFromClient(QString readedData)
 
 void MainWindow::on_writeButton_clicked()
 {
+    uiCoils.resize(2);
+    uiholdingRegisters.resize(2);
     int startAddress = ui->writeAddress->value();
     // do not go beyond 10 entries
     int numberOfEntries = qMin(ui->writeSize->currentText().toInt(), 10 - startAddress);
     switch (ui->writeTable->currentData().toInt()) {
     case 0:
+        qDebug() << "coil " << numberOfEntries ;
         if(numberOfEntries>1)
         {
-            uiCoils.setBit(1,ui->coilData1->isChecked());
-            uiCoils.setBit(2,ui->coilData2->isChecked());
+            uiCoils.setBit(0,ui->coilData1->isChecked());
+            uiCoils.setBit(1,ui->coilData2->isChecked());
             modBusObj.setMultipleCoil(startAddress, numberOfEntries, uiCoils);
         }
         else if (numberOfEntries==1)
         {
+            qDebug() << "coil umberOfEntries==1 " << numberOfEntries ;
             modBusObj.setSingleCoil(startAddress, ui->coilData1->isChecked());
         }
         break;
diff --git a/serialConnectionManager/modbusmaster.cpp b/serialConnectionManager/modbusmaster.cpp
index 397f977..0913c64 100644
--- a/serialConnectionManager/modbusmaster.cpp
+++ b/serialConnectionManager/modbusmaster.cpp
@@ -6,6 +6,8 @@
 enum { NumColumn = 0, CoilsColumn = 1, HoldingColumn = 2, ColumnCount = 3, RowCount = 10 };
 modBusMaster::modBusMaster(QObject *parent) : QObject(parent)
 {
+    m_coils.resize(2);
+    m_holdingRegisters.resize(2);
 
 }
 
@@ -71,8 +73,10 @@ void modBusMaster::setSingleCoil(int startAddress,bool coilFlag)
 {
     if (!modbusDevice)
         return;
-    m_coils.clear();
-    m_coils.setBit(1,coilFlag);
+    qDebug() << " ---- setSingleCoil " ;
+    m_coils.clearBit(2);
+    m_coils.setBit(0,coilFlag);
+    qDebug() << " ---- setSingleCoil coilFlag "  <<coilFlag;
     writeRequest(QModbusDataUnit::RegisterType::Coils,  startAddress, 1);
 
 }
@@ -82,7 +86,6 @@ void modBusMaster::setMultipleCoil(int startAddress, quint16 writeSize, QBitArra
     if (!modbusDevice)
         return;
     m_holdingRegisters.clear();
-    m_coils.clear();
     m_coils = someCoilFlags;
     writeRequest(QModbusDataUnit::RegisterType::Coils,  startAddress, writeSize);
 }
@@ -138,7 +141,6 @@ void modBusMaster::getHoldingRegister(int startAddress, quint16 readSize)
 
 void  modBusMaster::readRequest(QModbusDataUnit::RegisterType registerType, int startAddress, quint16 readSize)
 {
-    qDebug() << " first of readRequest";
     auto table =registerType;
     reply=modbusDevice->sendReadRequest(QModbusDataUnit(table, startAddress, readSize), serverId) ;
     if (reply)
@@ -159,9 +161,11 @@ void  modBusMaster::readRequest(QModbusDataUnit::RegisterType registerType, int
 
 void modBusMaster::writeRequest(QModbusDataUnit::RegisterType registerType, int startAddress, quint16 writeSize)
 {
+    qDebug() << " ---- setSingleCoil coilFlag writeRequest ";
     auto table =registerType;
     Q_ASSERT(startAddress >= 0 && startAddress < 10);
     QModbusDataUnit writeUnit = QModbusDataUnit(table, startAddress, writeSize);
+    qDebug() << " ---- writeUnit.valueCount()" << writeUnit.valueCount();
     for (int i = 0; i < writeUnit.valueCount(); i++) {
         if (table == QModbusDataUnit::Coils)
             writeUnit.setValue(i,  m_coils[i + writeUnit.startAddress()]);