diff --git a/ChangeLog b/ChangeLog
index 12b3ccda..3d2c3d14 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -15754,3 +15754,7 @@
 2017-05-02 Fred Gleason <fredg@paravelsystems.com>
 	* Fixed a bug that caused RDCartSlots to fail to rotate cuts when
 	replaying a cart without a reload.
+2017-05-03 Fred Gleason <fredg@paravelsystems.com>
+	* Added an 'RDMatrix::Modbus' element to the 'RDMatrix::Type enum.
+	* Implemented a Modbus TCP switcher driver in 'ripcd/modbus.cpp' and
+	'ripcd/modbus.h'.
diff --git a/docs/SWITCHERS.txt b/docs/SWITCHERS.txt
index 1a12f688..f7d95f5e 100644
--- a/docs/SWITCHERS.txt
+++ b/docs/SWITCHERS.txt
@@ -24,6 +24,7 @@ LiveWire LWRP GPIO
 LiveWire Multicast GPIO
 Local Audio Adapter
 Logitek vGuest
+Modbus TCP
 Quartz Electronics Type 1 Routing Protocol
 Ross NK Video Switchers (via SCP/A Serial Interface)
 Serial Port Modem Control Lines
@@ -580,6 +581,19 @@ such as faders feeds, not just GPIO) are mapped to logical Rivendell
 GPIO lines by means of their Logitek Engine, Device and Buss numbers.
 
 
+----------------------------------------------------------------------------
+Driver Name: Modbus TCP
+
+Supported RML Commands:
+  GPI Enable ('GE')
+  GPI Set ('GI')
+
+GENERAL NOTES:
+This driver supports GPI devices that use the industry-standard Modbus TCP
+protocol at TCP port 502. The device to be controlled should be configured
+to use Modbus ID #1. For more information on Modbus, see http://www.modbus.org/.
+
+
 ----------------------------------------------------------------------------
 Quartz Electronics Type 1 Routing Protocol
 
diff --git a/lib/rdmatrix.cpp b/lib/rdmatrix.cpp
index 2c5c8951..2941c8f9 100644
--- a/lib/rdmatrix.cpp
+++ b/lib/rdmatrix.cpp
@@ -66,7 +66,8 @@ bool __mx_primary_controls[RDMatrix::LastType][RDMatrix::LastControl]=
     {0,1,1,1,0,0,1,1,0,0,0,1,1,0,0,0,1,1,1,1,0,0,0,0,1,0,0,0,0},  // SAS 16000
     {0,1,0,0,0,0,0,0,1,0,0,1,1,0,0,0,1,1,0,0,0,0,0,0,0,0,0,0,0},  // Ross NK/SCP
     {0,1,0,0,0,0,0,0,0,0,0,0,0,0,0,0,1,1,1,1,0,0,0,0,0,0,0,0,0},  // BT ADMS 44.22
-    {0,1,0,0,0,0,0,0,0,0,0,0,0,0,0,0,1,1,1,1,0,0,0,0,0,0,0,0,0}   // BT SS 4.1 MLR
+    {0,1,0,0,0,0,0,0,0,0,0,0,0,0,0,0,1,1,1,1,0,0,0,0,0,0,0,0,0},  // BT SS 4.1 MLR
+    {0,0,1,1,0,0,0,0,0,0,0,0,0,1,1,0,0,0,1,1,0,0,0,0,0,0,0,0,0}   // Modbus
   };
 bool __mx_backup_controls[RDMatrix::LastType][RDMatrix::LastControl]=
   {
@@ -109,7 +110,8 @@ bool __mx_backup_controls[RDMatrix::LastType][RDMatrix::LastControl]=
     {0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0},  // SAS 16000
     {0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0},  // ROSS NK/SCP
     {0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0},  // BT ADMS 44.22
-    {0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0}   // BT SS 4.1 MLR
+    {0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0},  // BT SS 4.1 MLR
+    {0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0}   // Modbus
   };
 
 int __mx_default_values[RDMatrix::LastType][RDMatrix::LastControl]=
@@ -153,7 +155,8 @@ int __mx_default_values[RDMatrix::LastType][RDMatrix::LastControl]=
     {0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,1,0},   // SAS 16000
     {0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,1,0},  // Ross NK/SCP
     {0,0,0,0,0,0,0,0,0,0,0,8,2,16,13,0,0,0,0,0,0,0,0,0,0,0,0,1,0}, // BT ADMS 44.22
-    {0,0,0,0,0,0,0,0,0,0,0,4,1,8,0,0,0,0,0,0,0,0,0,0,0,0,0,1,0}  // BT SS 4.1 MLR
+    {0,0,0,0,0,0,0,0,0,0,0,4,1,8,0,0,0,0,0,0,0,0,0,0,0,0,0,1,0}, // BT SS 4.1 MLR
+    {1,0,0,502,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,1,0}  // Modbus
   };
 
 RDMatrix::RDMatrix(const QString &station,int matrix)
@@ -717,6 +720,10 @@ QString RDMatrix::typeString(RDMatrix::Type type)
 	return QString("BroadcastTools SS 4.1 MLR");
 	break;
 
+      case RDMatrix::Modbus:
+	return QString("Modbus TCP");
+	break;
+
       default:
 	return QString("Unknown Type");
 	break;
diff --git a/lib/rdmatrix.h b/lib/rdmatrix.h
index 7be22d73..fa9866af 100644
--- a/lib/rdmatrix.h
+++ b/lib/rdmatrix.h
@@ -2,7 +2,7 @@
 //
 // Abstract a Rivendell Switcher Matrix
 //
-//   (C) Copyright 2002-2016 Fred Gleason <fredg@paravelsystems.com>
+//   (C) Copyright 2002-2017 Fred Gleason <fredg@paravelsystems.com>
 //
 //   This program is free software; you can redistribute it and/or modify
 //   it under the terms of the GNU General Public License version 2 as
@@ -38,7 +38,7 @@ class RDMatrix
 	     BtSrc16=24,Harlond=25,Acu1p=26,LiveWireMcastGpio=27,Am16=28,
 	     LiveWireLwrpGpio=29,BtSentinel4Web=30,BtGpi16=31,ModemLines=32,
 	     SoftwareAuthority=33,Sas16000=34,RossNkScp=35,BtAdms4422=36,
-	     BtSs41Mlr=37,LastType=38};
+	     BtSs41Mlr=37,Modbus=38,LastType=39};
   enum Endpoint {Input=0,Output=1};
   enum Mode {Stereo=0,Left=1,Right=2};
   enum VguestAttribute {VguestEngine=0,VguestDevice=1,VguestSurface=2,
diff --git a/ripcd/Makefile.am b/ripcd/Makefile.am
index e9c82a01..188132fb 100644
--- a/ripcd/Makefile.am
+++ b/ripcd/Makefile.am
@@ -57,6 +57,7 @@ dist_ripcd_SOURCES = acu1p.cpp acu1p.h\
                      local_gpio.cpp local_gpio.h\
                      local_macros.cpp maint_routines.cpp\
                      loaddrivers.cpp\
+                     modbus.cpp modbus.h\
                      modemlines.cpp modemlines.h\
                      quartz1.cpp quartz1.h\
                      ripcd.cpp ripcd.h globals.h\
@@ -100,6 +101,7 @@ nodist_ripcd_SOURCES = moc_am16.cpp\
                        moc_livewire_mcastgpio.cpp\
                        moc_local_audio.cpp\
                        moc_local_gpio.cpp\
+                       moc_modbus.cpp\
                        moc_modemlines.cpp\
                        moc_quartz1.cpp\
                        moc_ripcd.cpp\
diff --git a/ripcd/loaddrivers.cpp b/ripcd/loaddrivers.cpp
index c1f91593..7a46f6e7 100644
--- a/ripcd/loaddrivers.cpp
+++ b/ripcd/loaddrivers.cpp
@@ -47,6 +47,7 @@
 #include <livewire_mcastgpio.h>
 #include <local_audio.h>
 #include <local_gpio.h>
+#include <modbus.h>
 #include <modemlines.h>
 #include <quartz1.h>
 #include <rossnkscp.h>
@@ -165,6 +166,10 @@ bool MainObject::LoadSwitchDriver(int matrix_num)
     ripcd_switcher[matrix_num]=new VGuest(matrix,this);
     break;
 
+  case RDMatrix::Modbus:
+    ripcd_switcher[matrix_num]=new Modbus(matrix,this);
+    break;
+
   case RDMatrix::ModemLines:
     ripcd_switcher[matrix_num]=new ModemLines(matrix,this);
     break;
diff --git a/ripcd/modbus.cpp b/ripcd/modbus.cpp
new file mode 100644
index 00000000..83c46ee6
--- /dev/null
+++ b/ripcd/modbus.cpp
@@ -0,0 +1,250 @@
+// modbus.cpp
+//
+// A Rivendell switcher driver for Modbus TCP
+//
+//   (C) Copyright 2017 Fred Gleason <fredg@paravelsystems.com>
+//
+//   This program is free software; you can redistribute it and/or modify
+//   it under the terms of the GNU General Public License version 2 as
+//   published by the Free Software Foundation.
+//
+//   This program is distributed in the hope that it will be useful,
+//   but WITHOUT ANY WARRANTY; without even the implied warranty of
+//   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+//   GNU General Public License for more details.
+//
+//   You should have received a copy of the GNU General Public
+//   License along with this program; if not, write to the Free Software
+//   Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
+//
+
+#include <syslog.h>
+
+#include "modbus.h"
+
+Modbus::Modbus(RDMatrix *matrix,QObject *parent)
+  : Switcher(matrix,parent)
+{
+  modbus_istate=0;
+  modbus_watchdog_active=false;
+
+  modbus_gpis=matrix->gpis();
+  modbus_input_bytes=modbus_gpis/8;
+  if((modbus_gpis%8)!=0) {
+    modbus_input_bytes++;
+  }
+  for(int i=0;i<modbus_input_bytes;i++) {
+    modbus_input_states.push_back(0);
+  }
+  modbus_gpos=matrix->gpos();
+  modbus_ip_address=matrix->ipAddress(RDMatrix::Primary);
+  modbus_ip_port=matrix->ipPort(RDMatrix::Primary);
+
+  modbus_socket=new QSocket(this);
+  connect(modbus_socket,SIGNAL(connected()),this,SLOT(connectedData()));
+  connect(modbus_socket,SIGNAL(readyRead()),this,SLOT(readyReadData()));
+  connect(modbus_socket,SIGNAL(error(int)),this,SLOT(errorData(int)));
+  modbus_socket->connectToHost(modbus_ip_address.toString(),modbus_ip_port);
+
+  modbus_watchdog_timer=new QTimer(this);
+  connect(modbus_watchdog_timer,SIGNAL(timeout()),this,SLOT(watchdogData()));
+}
+
+
+Modbus::~Modbus()
+{
+  delete modbus_watchdog_timer;
+  delete modbus_socket;
+}
+
+
+RDMatrix::Type Modbus::type()
+{
+  return RDMatrix::Modbus;
+}
+
+
+unsigned Modbus::gpiQuantity()
+{
+  return modbus_gpis;
+}
+
+
+unsigned Modbus::gpoQuantity()
+{
+  return modbus_gpos;
+}
+
+
+bool Modbus::primaryTtyActive()
+{
+  return false;
+}
+
+
+bool Modbus::secondaryTtyActive()
+{
+  return false;
+}
+
+
+void Modbus::processCommand(RDMacro *cmd)
+{
+}
+
+
+void Modbus::connectedData()
+{
+  syslog(LOG_INFO,
+	 "connection to Modbus device at %s:%u established",
+	 (const char *)modbus_ip_address.toString(),0xffff&modbus_ip_port);
+  modbus_watchdog_active=false;
+  PollInputs();
+}
+
+
+void Modbus::readyReadData()
+{
+  char data[1501];
+  int n;
+  char byte;
+  uint16_t len;
+  //  char id;
+  char count=0;
+  int base=0;
+
+  while((n=modbus_socket->readBlock(data,1500))>0) {
+    for(int i=0;i<n;i++) {
+      byte=0xff&data[i];
+      switch(modbus_istate) {
+      case 0:   // Transaction Identifier
+	modbus_istate=1;
+	break;
+
+      case 1:
+	modbus_istate=2;
+	break;
+
+      case 2:   // Protocol Identifier
+	if(byte==0) {
+	  modbus_istate=3;
+	}
+	else {
+	  modbus_istate=0;
+	}
+	break;
+
+      case 3:   // Protocol Identifier
+	if(byte==0) {
+	  modbus_istate=4;
+	}
+	else {
+	  modbus_istate=0;
+	}
+	break;
+
+      case 4:   // Message Length
+	len=byte<<8;
+	modbus_istate=5;
+	break;
+
+      case 5:   // Message Length
+	len+=byte;
+	modbus_istate=6;
+	break;
+
+      case 6:   // Modbus ID
+	//	id=byte;
+	modbus_istate=7;
+	break;
+
+      case 7:   // Function Code
+	if(byte==0x02) {
+	  modbus_istate=8;
+	}
+	else {
+	  modbus_istate=0;
+	}
+	break;
+
+      case 8:   // Byte Count
+	count=byte;
+	modbus_istate=9;
+	break;
+
+      case 9:   // Input Status
+	base=modbus_input_bytes-count;
+	ProcessInputByte(byte,base);
+	if(--count==0) {
+	  PollInputs();
+	  modbus_istate=0;
+	}
+	break;
+      }
+    }
+  }
+}
+
+
+void Modbus::errorData(int err)
+{
+  watchdogData();
+}
+
+
+void Modbus::watchdogData()
+{
+  if(!modbus_watchdog_active) {
+    syslog(LOG_WARNING,
+	   "connection to Modbus device at %s:%u lost, attempting reconnect",
+	   (const char *)modbus_ip_address.toString(),0xffff&modbus_ip_port);
+    modbus_watchdog_active=true;
+  }
+  modbus_socket->close();
+  modbus_socket->connectToHost(modbus_ip_address.toString(),modbus_ip_port);
+}
+
+
+void Modbus::ProcessInputByte(char byte,int base)
+{
+  char mask=byte^modbus_input_states[base];
+  for(int i=0;i<8;i++) {
+    if(((1<<i)&mask)!=0) {
+      int line=8*base+i;
+      if(line<modbus_gpis) {
+	emit gpiChanged(matrixNumber(),line,((1<<i)&byte)!=0);
+      }
+    }
+  }
+  modbus_input_states[base]=byte;
+}
+
+
+void Modbus::PollInputs()
+{
+  printf("HERE1\n");
+  char msg[12];
+  msg[0]=0x88;  // Transaction Identifier
+  msg[1]=0x88;
+
+  msg[2]=0x00;  // Protocol Identifier
+  msg[3]=0x00;
+
+  msg[4]=0x00;  // Message Length
+  msg[5]=0x06;
+
+  msg[6]=0x01;  // Modbus ID
+
+  msg[7]=0x02;  // Function Code (Read Discrete Input)
+
+  msg[8]=0x00;  // Starting Address
+  msg[9]=0x00;
+
+  msg[10]=0xff&(modbus_gpis>>8);  // Quantity of Inputs
+  msg[11]=0xff&modbus_gpis;
+
+  modbus_socket->writeBlock(msg,12);
+  modbus_watchdog_timer->stop();
+  modbus_watchdog_timer->start(MODBUS_WATCHDOG_INTERVAL,true);
+  printf("HERE2\n");
+}
diff --git a/ripcd/modbus.h b/ripcd/modbus.h
new file mode 100644
index 00000000..e379219c
--- /dev/null
+++ b/ripcd/modbus.h
@@ -0,0 +1,72 @@
+// modbus.h
+//
+// A Rivendell switcher driver for Modbus TCP
+//
+//   (C) Copyright 2017 Fred Gleason <fredg@paravelsystems.com>
+//
+//   This program is free software; you can redistribute it and/or modify
+//   it under the terms of the GNU General Public License version 2 as
+//   published by the Free Software Foundation.
+//
+//   This program is distributed in the hope that it will be useful,
+//   but WITHOUT ANY WARRANTY; without even the implied warranty of
+//   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+//   GNU General Public License for more details.
+//
+//   You should have received a copy of the GNU General Public
+//   License along with this program; if not, write to the Free Software
+//   Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
+//
+
+#ifndef MODBUS_H
+#define MODBUS_H
+
+#include <vector>
+
+#include <qsocket.h>
+#include <qtimer.h>
+
+#include <rd.h>
+#include <rdmatrix.h>
+#include <rdmacro.h>
+
+#include <switcher.h>
+
+#define MODBUS_WATCHDOG_INTERVAL 1000
+
+class Modbus : public Switcher
+{
+ Q_OBJECT
+ public:
+  Modbus(RDMatrix *matrix,QObject *parent=0);
+  ~Modbus();
+  RDMatrix::Type type();
+  unsigned gpiQuantity();
+  unsigned gpoQuantity();
+  bool primaryTtyActive();
+  bool secondaryTtyActive();
+  void processCommand(RDMacro *cmd);
+
+ private slots:
+  void connectedData();
+  void readyReadData();
+  void errorData(int err);
+  void watchdogData();
+
+ private:
+  void ProcessInputByte(char byte,int base);
+  void PollInputs();
+  int modbus_istate;
+  int modbus_input_bytes;
+  std::vector<char> modbus_input_states;
+  QSocket *modbus_socket;
+  QTimer *modbus_watchdog_timer;
+  bool modbus_watchdog_active;
+  QHostAddress modbus_ip_address;
+  uint16_t modbus_ip_port;
+  int modbus_gpis;
+  int modbus_gpos;
+};
+
+
+#endif  // MODBUS_H