diff --git a/TODO b/TODO
index 008bc246f9a9a990641423655e53c2c2528c7954..b79ac5c181e1055f90e3e0d7d02bac666de27039 100644
--- a/TODO
+++ b/TODO
@@ -52,6 +52,7 @@ Version 1.5.0:
 * Implement CompleteAccess for SDO uploads.
 * Implement identifier parameter for cstruct command.
 * Implement sync delimiter for cstruct command.
+* Implement ecrt_master_deactivate() in userspace.
 
 Future issues:
 
diff --git a/include/ecrt.h b/include/ecrt.h
index b8d88e9996a7e713d6dd51335e000308fc4b840a..59b1d81c7d640819a77c3c5f2d5eba45f3dbcf0e 100644
--- a/include/ecrt.h
+++ b/include/ecrt.h
@@ -55,6 +55,7 @@
  *   ecrt_slave_config_sync_manager()).
  * - Added ecrt_slave_config_complete_sdo() method to download an SDO during
  *   configuration via CompleteAccess.
+ * - Added ecrt_master_deactivate() to remove the bus configuration.
  * - Added ecrt_open_master() and ecrt_master_reserve() separation for
  *   userspace.
  * - Added bus information interface (methods ecrt_master(),
@@ -682,6 +683,18 @@ int ecrt_master_activate(
         ec_master_t *master /**< EtherCAT master. */
         );
 
+/** Deactivates the master.
+ *
+ * Removes the bus configuration. All objects created by
+ * ecrt_master_create_domain(), ecrt_master_slave_config(), ecrt_domain_data()
+ * ecrt_slave_config_create_sdo_request() and
+ * ecrt_slave_config_create_voe_handler() are freed, so pointers to them
+ * become invalid.
+ */
+void ecrt_master_deactivate(
+        ec_master_t *master /**< EtherCAT master. */
+        );
+
 /** Sends all datagrams in the queue.
  *
  * This method takes all datagrams, that have been queued for transmission,
diff --git a/master/cdev.c b/master/cdev.c
index a744bf76a9e6d46a7a952904e2baa5ef5451e2a3..c1ce6add5acb7f9ce7dae8ffd14d1788390b05bf 100644
--- a/master/cdev.c
+++ b/master/cdev.c
@@ -175,6 +175,7 @@ int ec_cdev_ioctl_master(
     data.eoe_handler_count = ec_master_eoe_handler_count(master);
 #endif
     data.phase = (uint8_t) master->phase;
+    data.active = (uint8_t) master->active;
     data.scan_busy = master->scan_busy;
     up(&master->master_sem);
 
diff --git a/master/ioctl.h b/master/ioctl.h
index 4e84df9ae62578e0a4d1f7b2350f657731584632..9753b31e3357f7dafcbabcfde20c5086861897e0 100644
--- a/master/ioctl.h
+++ b/master/ioctl.h
@@ -135,6 +135,7 @@ typedef struct {
     uint32_t eoe_handler_count;
 #endif
     uint8_t phase;
+    uint8_t active;
     uint8_t scan_busy;
     struct {
         uint8_t address[6];
diff --git a/master/master.c b/master/master.c
index 263cba0a6f9e96ea491eb9a438fcbec19f1cb4ea..d9b659d082403f0c2a0630c59f6a4452d784961f 100644
--- a/master/master.c
+++ b/master/master.c
@@ -121,6 +121,7 @@ int ec_master_init(ec_master_t *master, /**< EtherCAT master */
     init_MUTEX(&master->device_sem);
 
     master->phase = EC_ORPHANED;
+    master->active = 0;
     master->injection_seq_fsm = 0;
     master->injection_seq_rt = 0;
 
@@ -592,67 +593,17 @@ out_allow:
 
 /** Transition function from OPERATION to IDLE phase.
  */
-void ec_master_leave_operation_phase(ec_master_t *master
-                                    /**< EtherCAT master */)
+void ec_master_leave_operation_phase(
+        ec_master_t *master /**< EtherCAT master */
+        )
 {
-    ec_slave_t *slave;
-#ifdef EC_EOE
-    ec_eoe_t *eoe;
-#endif
+    if (master->active)
+        ecrt_master_deactivate(master);
 
     if (master->debug_level)
         EC_DBG("OPERATION -> IDLE.\n");
 
     master->phase = EC_IDLE;
-
-#ifdef EC_EOE
-    ec_master_eoe_stop(master);
-#endif
-    ec_master_thread_stop(master);
-    
-    master->send_cb = ec_master_internal_send_cb;
-    master->receive_cb = ec_master_internal_receive_cb;
-    master->cb_data = master;
-    
-    down(&master->master_sem);
-    ec_master_clear_domains(master);
-    ec_master_clear_slave_configs(master);
-    up(&master->master_sem);
-
-    for (slave = master->slaves;
-            slave < master->slaves + master->slave_count;
-            slave++) {
-
-        // set states for all slaves
-        ec_slave_request_state(slave, EC_SLAVE_STATE_PREOP);
-
-        // mark for reconfiguration, because the master could have no
-        // possibility for a reconfiguration between two sequential operation
-        // phases.
-        slave->force_config = 1;
-    }
-
-#ifdef EC_EOE
-    // ... but leave EoE slaves in OP
-    list_for_each_entry(eoe, &master->eoe_handlers, list) {
-        if (ec_eoe_is_open(eoe))
-            ec_slave_request_state(eoe->slave, EC_SLAVE_STATE_OP);
-    }
-#endif
-
-    master->app_time = 0ULL;
-    master->app_start_time = 0ULL;
-    master->has_start_time = 0;
-
-    if (ec_master_thread_start(master, ec_master_idle_thread,
-                "EtherCAT-IDLE"))
-        EC_WARN("Failed to restart master thread!\n");
-#ifdef EC_EOE
-    ec_master_eoe_start(master);
-#endif
-
-    master->allow_scan = 1;
-    master->allow_config = 1;
 }
 
 /*****************************************************************************/
@@ -1635,6 +1586,11 @@ int ecrt_master_activate(ec_master_t *master)
     if (master->debug_level)
         EC_DBG("ecrt_master_activate(master = 0x%x)\n", (u32) master);
 
+    if (master->active) {
+        EC_WARN("%s: Master already active!\n", __func__);
+        return 0;
+    }
+
     down(&master->master_sem);
 
     // finish all domains
@@ -1684,11 +1640,80 @@ int ecrt_master_activate(ec_master_t *master)
 
     master->allow_config = 1; // request the current configuration
     master->allow_scan = 1; // allow re-scanning on topology change
+    master->active = 1;
     return 0;
 }
 
 /*****************************************************************************/
 
+void ecrt_master_deactivate(ec_master_t *master)
+{
+    ec_slave_t *slave;
+#ifdef EC_EOE
+    ec_eoe_t *eoe;
+#endif
+
+    if (master->debug_level)
+        EC_DBG("ecrt_master_deactivate(master = 0x%x)\n", (u32) master);
+
+    if (!master->active) {
+        EC_WARN("%s: Master not active.\n", __func__);
+        return;
+    }
+
+#ifdef EC_EOE
+    ec_master_eoe_stop(master);
+#endif
+    ec_master_thread_stop(master);
+    
+    master->send_cb = ec_master_internal_send_cb;
+    master->receive_cb = ec_master_internal_receive_cb;
+    master->cb_data = master;
+    
+    down(&master->master_sem);
+    ec_master_clear_domains(master);
+    ec_master_clear_slave_configs(master);
+    up(&master->master_sem);
+
+    for (slave = master->slaves;
+            slave < master->slaves + master->slave_count;
+            slave++) {
+
+        // set states for all slaves
+        ec_slave_request_state(slave, EC_SLAVE_STATE_PREOP);
+
+        // mark for reconfiguration, because the master could have no
+        // possibility for a reconfiguration between two sequential operation
+        // phases.
+        slave->force_config = 1;
+    }
+
+#ifdef EC_EOE
+    // ... but leave EoE slaves in OP
+    list_for_each_entry(eoe, &master->eoe_handlers, list) {
+        if (ec_eoe_is_open(eoe))
+            ec_slave_request_state(eoe->slave, EC_SLAVE_STATE_OP);
+    }
+#endif
+
+    master->app_time = 0ULL;
+    master->app_start_time = 0ULL;
+    master->has_start_time = 0;
+
+    if (ec_master_thread_start(master, ec_master_idle_thread,
+                "EtherCAT-IDLE"))
+        EC_WARN("Failed to restart master thread!\n");
+#ifdef EC_EOE
+    ec_master_eoe_start(master);
+#endif
+
+    master->allow_scan = 1;
+    master->allow_config = 1;
+    master->active = 0;
+}
+
+/*****************************************************************************/
+
 void ecrt_master_send(ec_master_t *master)
 {
     ec_datagram_t *datagram, *n;
@@ -1903,6 +1928,7 @@ void ecrt_master_sync_slave_clocks(ec_master_t *master)
 
 EXPORT_SYMBOL(ecrt_master_create_domain);
 EXPORT_SYMBOL(ecrt_master_activate);
+EXPORT_SYMBOL(ecrt_master_deactivate);
 EXPORT_SYMBOL(ecrt_master_send);
 EXPORT_SYMBOL(ecrt_master_send_ext);
 EXPORT_SYMBOL(ecrt_master_receive);
diff --git a/master/master.h b/master/master.h
index 8070276723f342d8a017cdbd9995e45048e8b51e..c759ea928107b3b2f4f636f7726362e1065f92f0 100644
--- a/master/master.h
+++ b/master/master.h
@@ -108,6 +108,7 @@ struct ec_master {
     ec_fsm_master_t fsm; /**< Master state machine. */
     ec_datagram_t fsm_datagram; /**< Datagram used for state machines. */
     ec_master_phase_t phase; /**< Master phase. */
+    unsigned int active; /**< Master has been activated. */
     unsigned int injection_seq_fsm; /**< Datagram injection sequence number
                                       for the FSM side. */
     unsigned int injection_seq_rt; /**< Datagram injection sequence number
diff --git a/tool/CommandMaster.cpp b/tool/CommandMaster.cpp
index 636b4ae5ec5104b6bb6de20dc84a06fd8501e7b0..1460f4dc240e7a92b144180b6a008728b56378d8 100644
--- a/tool/CommandMaster.cpp
+++ b/tool/CommandMaster.cpp
@@ -91,6 +91,7 @@ void CommandMaster::execute(MasterDevice &m, const StringVector &args)
     }
 
     cout << endl
+        << "  Active: " << (data.active ? "yes" : "no") << endl
         << "  Slaves: " << data.slave_count << endl
         << "  Ethernet devices:" << endl;