diff --git a/CMakeLists.txt b/CMakeLists.txt
index e959b07..6bd620d 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -7,6 +7,7 @@ target_sources(grbl INTERFACE
  ${CMAKE_CURRENT_LIST_DIR}/gcode.c
  ${CMAKE_CURRENT_LIST_DIR}/machine_limits.c
  ${CMAKE_CURRENT_LIST_DIR}/messages.c
+ ${CMAKE_CURRENT_LIST_DIR}/modbus.c
  ${CMAKE_CURRENT_LIST_DIR}/motion_control.c
  ${CMAKE_CURRENT_LIST_DIR}/my_plugin.c
  ${CMAKE_CURRENT_LIST_DIR}/nuts_bolts.c
diff --git a/changelog.md b/changelog.md
index 64ded26..84fbead 100644
--- a/changelog.md
+++ b/changelog.md
@@ -1,18 +1,46 @@
 ## grblHAL changelog
 
+<a name="20230610"/>Build 20230610
+
+Core:
+
+Added virtual Modbus API. Some internal settings handling improvements.
+
+Drivers:
+
+* iMXRT1062, STM32F7xx and RP2040: added Modbus TCP network support.
+
+* STM32F1xx: rerouted _Reset_ signal as _Emergency stop_ per default. Can be overriden in _my_machine.h_ or by setting `COMPATIBILITY_LEVEL` > 1.
+
+* STM32F4xx, ESP32, SAM3X8E and MSP432P401R: minor changes to handle new location of Modbus API.
+
+Plugins:
+
+* Spindle: refactored and renamed Modbus RTU code as a driver implementation for the core Modbus API.
+
+* Networking: added Modbus TCP driver for core Modbus API with support for up to 8 devices. Default is four.  
+Added WIZNet support for Modbus TCP.  
+Modbus TCP is enabled by bit 2 in the `MODBUS_ENABLE` symbol in _my_machine.h_: `#define MOBUS_ENABLE 4`. This can be added to the previous define values for enabling Modbus RTU with or without RS 485 direction signal support.  
+__NOTE:__ The new core API only supports the Modbus RTU protocol, this will be translated to/from Modbus TCP by the driver implementation.  
+User code _can_ bypass the core API and transmit Modbus TCP messages directly if it wants/needs to.  
+__NOTE:__ VFD spindle Modbus communication will be routed to Modbus TCP if the VFD device id \(unit id\) matches the Modbus TCP device id.  
+For now this is untested and may lock up the controller since the networking stack comes up too late to avoid power up selftest \(POS\) failure.  
+To be addressed in a later revision if someone with a Modbus TCP capable spindle is willing to test.
+
+* Motors and encoder: updated for core setting handling improvements.
+
 <a name="20230607"/>Build 20230607
 
 Core:
 
 * Added initial support for macro based automatic tool changes (ATC).  
 Currently macros has to be stored on a SD card or in littlefs and [expression support](https://github.com/grblHAL/core/wiki/Expressions-and-flow-control) has to be enabled.
-
 * Added core events for file system mount/unmount.
 
 Plugins:
 
-* SD Card, macro plugin: Implemented automatic hook to tool change functions when tool change macros are found in the root mount directory.  
-Tool change macro: _tc.macro_, called on `M6`. \(required\)  
+* SD Card, macro plugin: implemented automatic hook to tool change functions when tool change macros are found in the root mount directory.  
+Tool change macro: _tc.macro_, called on `M6`. \(required\).  
 Tool select macro: _ts.macro_, called on `T`. \(optional\).  
 __NOTE:__ This functionality needs to be extensively tested by users having access to ATC hardware! [Discuss here](https://github.com/grblHAL/core/discussions/309).
 
diff --git a/driver_opts.h b/driver_opts.h
index 5a1530b..0dca407 100644
--- a/driver_opts.h
+++ b/driver_opts.h
@@ -218,6 +218,15 @@
 #endif
 #endif
 
+#define MODBUS_RTU_ENABLED     0b001
+#define MODBUS_RTU_DIR_ENABLED 0b010
+#define MODBUS_TCP_ENABLED     0b100
+
+#if MODBUS_ENABLE == 2
+#undef MOBUS_ENABLE
+#define MOBUS_ENABLE 0b011
+#endif
+
 #ifndef MODBUS_ENABLE
 #if VFD_ENABLE
 #define MODBUS_ENABLE       1
@@ -371,6 +380,9 @@
 #ifndef NETWORK_HTTP_PORT
 #define NETWORK_HTTP_PORT       80
 #endif
+#ifndef NETWORK_MODBUS_PORT
+#define NETWORK_MODBUS_PORT     502
+#endif
 #ifndef NETWORK_MQTT_PORT
 #define NETWORK_MQTT_PORT       1883
 #endif
diff --git a/grbl.h b/grbl.h
index f30773d..fcca688 100644
--- a/grbl.h
+++ b/grbl.h
@@ -42,7 +42,7 @@
 #else
 #define GRBL_VERSION "1.1f"
 #endif
-#define GRBL_BUILD 20230607
+#define GRBL_BUILD 20230610
 
 #define GRBL_URL "https://github.com/grblHAL"
 
diff --git a/maslow.c b/maslow.c
index 70ea8ea..414e396 100644
--- a/maslow.c
+++ b/maslow.c
@@ -101,6 +101,8 @@ static float get_axis_setting (setting_id_t setting);
 static void maslow_settings_load (void);
 static void maslow_settings_restore (void);
 
+#define AXIS_OPTS { .subgroups = On, .iterations = 1 }
+
 static const setting_detail_t maslow_settings[] = {
 #if maslow_MIXED_DRIVERS
     { Setting_maslowDriver, Group_MotorDriver, "maslow driver", NULL, Format_AxisMask, NULL, NULL, NULL, Setting_NonCore, &maslow.driver_enable.mask },
@@ -112,10 +114,10 @@ static const setting_detail_t maslow_settings[] = {
     { (setting_id_t)Maslow_MotorOffsetY, Group_MotorDriver, "Motor offset Y", "mm", Format_Decimal, "###0.0", NULL, NULL, Setting_NonCore, &maslow.motorOffsetY, NULL },
     { (setting_id_t)Maslow_AcorrScaling, Group_MotorDriver, "Acorr Scaling", NULL, Format_Decimal, "###0.0", NULL, NULL, Setting_NonCore, &maslow.XcorrScaling, NULL },
     { (setting_id_t)Maslow_BcorrScaling, Group_MotorDriver, "BcorrScaling", NULL, Format_Decimal, "###0.0", NULL, NULL, Setting_NonCore, &maslow.XcorrScaling, NULL },
-    { (setting_id_t)AxisSetting_MaslowKP, Group_Axis0, "?-axis KP", NULL, Format_Decimal, "###0.0", NULL, NULL, Setting_NonCoreFn, set_axis_setting, get_axis_setting },
-    { (setting_id_t)AxisSetting_MaslowKI, Group_Axis0, "?-axis KI", NULL, Format_Decimal, "###0.0", NULL, NULL, Setting_NonCoreFn, set_axis_setting, get_axis_setting },
-    { (setting_id_t)AxisSetting_MaslowKD, Group_Axis0, "?-axis KIt", NULL, Format_Decimal, "###0.0", NULL, NULL, Setting_NonCoreFn, set_axis_setting, get_axis_setting },
-    { (setting_id_t)AxisSetting_MaslowIMax, Group_Axis0, "?-axis I Max", "ma", Format_Decimal, "###0.0", NULL, NULL, Setting_NonCoreFn, set_axis_setting, get_axis_setting }
+    { (setting_id_t)AxisSetting_MaslowKP, Group_Axis0, "-axis KP", NULL, Format_Decimal, "###0.0", NULL, NULL, Setting_NonCoreFn, set_axis_setting, get_axis_setting, AXIS_OPTS },
+    { (setting_id_t)AxisSetting_MaslowKI, Group_Axis0, "-axis KI", NULL, Format_Decimal, "###0.0", NULL, NULL, Setting_NonCoreFn, set_axis_setting, get_axis_setting, AXIS_OPTS },
+    { (setting_id_t)AxisSetting_MaslowKD, Group_Axis0, "-axis KIt", NULL, Format_Decimal, "###0.0", NULL, NULL, Setting_NonCoreFn, set_axis_setting, get_axis_setting, AXIS_OPTS },
+    { (setting_id_t)AxisSetting_MaslowIMax, Group_Axis0, "-axis I Max", "ma", Format_Decimal, "###0.0", NULL, NULL, Setting_NonCoreFn, set_axis_setting, get_axis_setting, AXIS_OPTS }
 };
 
 static void maslow_settings_save (void)
diff --git a/modbus.c b/modbus.c
new file mode 100644
index 0000000..186ccfd
--- /dev/null
+++ b/modbus.c
@@ -0,0 +1,89 @@
+/*
+
+  modbus.h - a lightweight ModBus implementation, interface wrapper
+
+  Part of grblHAL
+
+  Copyright (c) 2023 Terje Io
+
+  Grbl is free software: you can redistribute it and/or modify
+  it under the terms of the GNU General Public License as published by
+  the Free Software Foundation, either version 3 of the License, or
+  (at your option) any later version.
+
+  Grbl 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 Grbl.  If not, see <http://www.gnu.org/licenses/>.
+
+*/
+
+#include "modbus.h"
+
+#include <string.h>
+
+#define N_MODBUS_API 2
+
+static uint_fast16_t n_api = 0, tcp_api = N_MODBUS_API, rtu_api = N_MODBUS_API;
+static modbus_api_t modbus[N_MODBUS_API] = {0};
+
+bool modbus_isup (void)
+{
+    bool ok = n_api > 0;
+    uint_fast16_t idx = n_api;
+
+    if(idx) do {
+        ok &= modbus[--idx].is_up();
+    } while(idx);
+
+    return ok;
+}
+
+bool modbus_enabled (void)
+{
+    return n_api > 0;
+}
+
+void modbus_flush_queue (void)
+{
+    uint_fast16_t idx = n_api;
+
+    if(idx) do {
+        modbus[--idx].flush_queue();
+    } while(idx);
+}
+
+void modbus_set_silence (const modbus_silence_timeout_t *timeout)
+{
+    if(rtu_api != N_MODBUS_API)
+        modbus[rtu_api].set_silence(timeout);
+}
+
+bool modbus_send (modbus_message_t *msg, const modbus_callbacks_t *callbacks, bool block)
+{
+    bool ok = false;
+
+    if(tcp_api != N_MODBUS_API)
+        ok = modbus[tcp_api].send(msg, callbacks, block);
+
+    return ok || (rtu_api != N_MODBUS_API && modbus[rtu_api].send(msg, callbacks, block));
+}
+
+bool modbus_register_api (const modbus_api_t *api)
+{
+    bool ok;
+
+    if((ok = n_api < N_MODBUS_API)) {
+        memcpy(&modbus[n_api], api, sizeof(modbus_api_t));
+        if(api->interface == Modbus_InterfaceTCP)
+            tcp_api = n_api;
+        else if(api->interface == Modbus_InterfaceRTU)
+            rtu_api = n_api;
+        n_api++;
+    }
+
+    return ok;
+}
diff --git a/modbus.h b/modbus.h
new file mode 100644
index 0000000..d51880b
--- /dev/null
+++ b/modbus.h
@@ -0,0 +1,101 @@
+/*
+
+  modbus.h - a lightweight ModBus implementation
+
+  Part of grblHAL
+
+  Copyright (c) 2023 Terje Io
+
+  Grbl is free software: you can redistribute it and/or modify
+  it under the terms of the GNU General Public License as published by
+  the Free Software Foundation, either version 3 of the License, or
+  (at your option) any later version.
+
+  Grbl 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 Grbl.  If not, see <http://www.gnu.org/licenses/>.
+
+*/
+
+#ifndef _MODBUS_H_
+#define _MODBUS_H_
+
+#ifndef MODBUS_MAX_ADU_SIZE
+#define MODBUS_MAX_ADU_SIZE 10
+#endif
+#ifndef MODBUS_QUEUE_LENGTH
+#define MODBUS_QUEUE_LENGTH 8
+#endif
+
+#include <stdint.h>
+#include <stdbool.h>
+
+typedef enum {
+    Modbus_InterfaceRTU = 0,
+    Modbus_InterfaceASCII,
+    Modbus_InterfaceTCP
+} modbus_if_t;
+
+typedef enum {
+    ModBus_ReadCoils = 1,
+    ModBus_ReadDiscreteInputs = 2,
+    ModBus_ReadHoldingRegisters = 3,
+    ModBus_ReadInputRegisters = 4,
+    ModBus_WriteCoil = 5,
+    ModBus_WriteRegister = 6,
+    ModBus_ReadExceptionStatus = 7,
+    ModBus_Diagnostics = 8,
+    ModBus_WriteCoils = 15,
+    ModBus_WriteRegisters = 16
+} modbus_function_t;
+
+typedef struct {
+    void *context;
+    bool crc_check;
+    uint8_t tx_length;
+    uint8_t rx_length;
+    char adu[MODBUS_MAX_ADU_SIZE];
+} modbus_message_t;
+
+typedef struct {
+    void (*on_rx_packet)(modbus_message_t *msg);
+    void (*on_rx_exception)(uint8_t code, void *context);
+} modbus_callbacks_t;
+
+typedef union {
+    uint16_t timeout[6];
+    struct {
+        uint16_t b2400;
+        uint16_t b4800;
+        uint16_t b9600;
+        uint16_t b19200;
+        uint16_t b38400;
+        uint16_t b115200;
+    };
+} modbus_silence_timeout_t;
+
+typedef bool (*modbus_is_up_ptr)(void);
+typedef void (*modbus_flush_queue_ptr)(void);
+typedef void (*modbus_set_silence_ptr)(const modbus_silence_timeout_t *timeout);
+typedef bool (*modbus_send_ptr)(modbus_message_t *msg, const modbus_callbacks_t *callbacks, bool block);
+
+typedef struct {
+    modbus_if_t interface;
+    modbus_is_up_ptr is_up;
+    modbus_flush_queue_ptr flush_queue;
+    modbus_set_silence_ptr set_silence;
+    modbus_send_ptr send;
+} modbus_api_t;
+
+bool modbus_isup (void);
+bool modbus_enabled (void);
+void modbus_flush_queue (void);
+void modbus_set_silence (const modbus_silence_timeout_t *timeout);
+bool modbus_send (modbus_message_t *msg, const modbus_callbacks_t *callbacks, bool block);
+bool modbus_register_api (const modbus_api_t *api);
+
+#endif
diff --git a/plugins.h b/plugins.h
index de6bfa3..9e2a9e0 100644
--- a/plugins.h
+++ b/plugins.h
@@ -136,6 +136,20 @@ typedef struct {
     uint32_t rx_timeout;
 } modbus_settings_t;
 
+#define MODBUS_TCP_SETTINGS_INCREMENT 5
+
+typedef enum {
+    Setting_ModbusIpAddress = 0,
+    Setting_ModbusPort      = 1,
+    Setting_ModbusId        = 2
+} modbus_tcp_setting_id_t;
+
+typedef struct {
+    char ip[16];
+    uint16_t port;
+    uint8_t id;
+} modbus_tcp_settings_t;
+
 // Quadrature encoder interface
 
 typedef enum {
diff --git a/plugins_init.h b/plugins_init.h
index 12a2a52..6a94f48 100644
--- a/plugins_init.h
+++ b/plugins_init.h
@@ -28,9 +28,9 @@
     trinamic_init();
 #endif
 
-#if MODBUS_ENABLE
-    extern void modbus_init (void);
-    modbus_init();
+#if MODBUS_ENABLE && MODBUS_ENABLE & 0x01
+    extern void modbus_rtu_init (void);
+    modbus_rtu_init();
 #endif
 
 #if CANBUS_ENABLE
diff --git a/report.c b/report.c
index 0923463..05edef9 100644
--- a/report.c
+++ b/report.c
@@ -1427,8 +1427,23 @@ static void write_quoted (const char *s, const char *sep)
         hal.stream.write(sep);
 }
 
+static void write_name (const char *s, uint_fast8_t offset)
+{
+    char *q = hal.stream.write_n ? strchr(s, '?') : NULL;
+
+    if(q) {
+        if(q != s)
+            hal.stream.write_n(s, q - s);
+        hal.stream.write(uitoa(offset + 1));
+        hal.stream.write(q + 1);
+    } else
+        hal.stream.write(s);
+}
+
 static void report_settings_detail (settings_format_t format, const setting_detail_t *setting, uint_fast8_t offset)
 {
+    uint_fast8_t suboffset = setting->flags.subgroups ? offset / setting->flags.increment : offset;
+
     switch(format)
     {
         case SettingsFormat_HumanReadable:
@@ -1437,7 +1452,7 @@ static void report_settings_detail (settings_format_t format, const setting_deta
             hal.stream.write(": ");
             if(setting->group == Group_Axis0)
                 hal.stream.write(axis_letter[offset]);
-            hal.stream.write(setting->name[0] == '?' ? &setting->name[1] : setting->name); // temporary hack for ? prefix...
+            write_name(setting->name, suboffset);
 
             switch(setting_datatype_to_external(setting->datatype)) {
 
@@ -1526,11 +1541,11 @@ static void report_settings_detail (settings_format_t format, const setting_deta
             hal.stream.write("[SETTING:");
             hal.stream.write(uitoa(setting->id + offset));
             hal.stream.write(vbar);
-            hal.stream.write(uitoa(setting->group + (setting->group == Group_Axis0 ? offset : 0)));
+            hal.stream.write(uitoa(setting->group + (setting->flags.subgroups ? suboffset : 0)));
             hal.stream.write(vbar);
             if(setting->group == Group_Axis0)
                 hal.stream.write(axis_letter[offset]);
-            hal.stream.write(setting->name[0] == '?' ? &setting->name[1] : setting->name); // temporary hack for ? prefix...
+            write_name(setting->name, suboffset);
             hal.stream.write(vbar);
             if(setting->unit)
                 hal.stream.write(setting->unit);
@@ -1558,7 +1573,7 @@ static void report_settings_detail (settings_format_t format, const setting_deta
                 hal.stream.write("\"");
                 if(setting->group == Group_Axis0)
                     hal.stream.write(axis_letter[offset]);
-                hal.stream.write(setting->name[0] == '?' ? &setting->name[1] : setting->name); // temporary hack for ? prefix...
+                write_name(setting->name, suboffset);
                 hal.stream.write("\",");
                 if(setting->unit) {
                     write_quoted(setting->unit, ",");
@@ -1582,7 +1597,7 @@ static void report_settings_detail (settings_format_t format, const setting_deta
 
                 if(setting->group == Group_Axis0)
                     hal.stream.write(axis_letter[offset]);
-                hal.stream.write(setting->name[0] == '?' ? &setting->name[1] : setting->name); // temporary hack for ? prefix...
+                write_name(setting->name, suboffset);
 
                 hal.stream.write("\t");
 
@@ -1949,7 +1964,7 @@ static void print_setting_group (const setting_group_detail_t *group, char *pref
             hal.stream.write(vbar);
             hal.stream.write(group->name);
             hal.stream.write("]" ASCII_EOL);
-        } else if(group->id != Group_Root && settings_is_group_available(group->id)) {
+        } else if(group->id != Group_Root) {
             hal.stream.write(prefix);
             hal.stream.write(group->name);
             hal.stream.write(ASCII_EOL);
@@ -1959,12 +1974,23 @@ static void print_setting_group (const setting_group_detail_t *group, char *pref
 
 static int cmp_setting_group_id (const void *a, const void *b)
 {
-    return (*(setting_detail_t **)(a))->id - (*(setting_detail_t **)(b))->id;
+    return (*(setting_group_detail_t **)(a))->id - (*(setting_group_detail_t **)(b))->id;
 }
 
 static int cmp_setting_group_name (const void *a, const void *b)
 {
-    return strcmp((*(setting_detail_t **)(a))->name, (*(setting_detail_t **)(b))->name);
+    return strcmp((*(setting_group_detail_t **)(a))->name, (*(setting_group_detail_t **)(b))->name);
+}
+
+static bool group_is_dup (setting_group_detail_t **groups, setting_group_t group)
+{
+    while(*groups) {
+        if((*groups)->id == group)
+            return true;
+        groups++;
+    }
+
+    return false;
 }
 
 status_code_t report_setting_group_details (bool by_id, char *prefix)
@@ -1984,8 +2010,10 @@ status_code_t report_setting_group_details (bool by_id, char *prefix)
         uint_fast16_t idx;
 
         do {
-            for(idx = 0; idx < details->n_groups; idx++)
-                *group++ = (setting_group_detail_t *)&details->groups[idx];
+            for(idx = 0; idx < details->n_groups; idx++) {
+                if(!group_is_dup(all_groups, details->groups[idx].id))
+                    *group++ = (setting_group_detail_t *)&details->groups[idx];
+            }
         } while((details = details->next));
 
         qsort(all_groups, n_groups, sizeof(setting_group_detail_t *), by_id ? cmp_setting_group_id : cmp_setting_group_name);
diff --git a/settings.c b/settings.c
index fea71e7..3b3b2cb 100644
--- a/settings.c
+++ b/settings.c
@@ -304,51 +304,56 @@ PROGMEM const settings_t defaults = {
     .safety_door.coolant_on_delay = DEFAULT_SAFETY_DOOR_COOLANT_DELAY
 };
 
+static bool group_is_available (const setting_group_detail_t *group)
+{
+    return true;
+}
+
 PROGMEM static const setting_group_detail_t setting_group_detail [] = {
-     { Group_Root, Group_Root, "Root"},
-     { Group_Root, Group_General, "General"},
-     { Group_Root, Group_ControlSignals, "Control signals"},
-     { Group_Root, Group_Limits, "Limits"},
-     { Group_Limits, Group_Limits_DualAxis, "Dual axis"},
-     { Group_Root, Group_Coolant, "Coolant"},
-     { Group_Root, Group_Spindle, "Spindle"},
-     { Group_Spindle, Group_Spindle_Sync, "Spindle sync"},
-     { Group_Root, Group_Toolchange, "Tool change"},
-     { Group_Root, Group_Homing, "Homing"},
-     { Group_Root, Group_Probing, "Probing"},
-     { Group_Root, Group_SafetyDoor, "Safety door"},
+     { Group_Root, Group_Root, "Root", group_is_available },
+     { Group_Root, Group_General, "General", group_is_available },
+     { Group_Root, Group_ControlSignals, "Control signals" },
+     { Group_Root, Group_Limits, "Limits" },
+     { Group_Limits, Group_Limits_DualAxis, "Dual axis" },
+     { Group_Root, Group_Coolant, "Coolant" },
+     { Group_Root, Group_Spindle, "Spindle" },
+     { Group_Spindle, Group_Spindle_Sync, "Spindle sync" },
+     { Group_Root, Group_Toolchange, "Tool change" },
+     { Group_Root, Group_Homing, "Homing" },
+     { Group_Root, Group_Probing, "Probing" },
+     { Group_Root, Group_SafetyDoor, "Safety door" },
      { Group_Root, Group_Jogging, "Jogging"},
-     { Group_Root, Group_Stepper, "Stepper"},
-     { Group_Root, Group_MotorDriver, "Stepper driver"},
-     { Group_Root, Group_Axis, "Axis"},
-     { Group_Axis, Group_XAxis, "X-axis"},
-     { Group_Axis, Group_YAxis, "Y-axis"},
-     { Group_Axis, Group_ZAxis, "Z-axis"},
+     { Group_Root, Group_Stepper, "Stepper" },
+     { Group_Root, Group_MotorDriver, "Stepper driver" },
+     { Group_Root, Group_Axis, "Axis", group_is_available },
+     { Group_Axis, Group_XAxis, "X-axis", group_is_available },
+     { Group_Axis, Group_YAxis, "Y-axis", group_is_available },
+     { Group_Axis, Group_ZAxis, "Z-axis", group_is_available },
 #if !AXIS_REMAP_ABC2UVW
   #ifdef A_AXIS
-     { Group_Axis, Group_AAxis, "A-axis"},
+     { Group_Axis, Group_AAxis, "A-axis", group_is_available },
   #endif
   #ifdef B_AXIS
-     { Group_Axis, Group_BAxis, "B-axis"},
+     { Group_Axis, Group_BAxis, "B-axis", group_is_available },
   #endif
   #ifdef C_AXIS
-     { Group_Axis, Group_CAxis, "C-axis"},
+     { Group_Axis, Group_CAxis, "C-axis", group_is_available },
   #endif
   #ifdef U_AXIS
-     { Group_Axis, Group_UAxis, "U-axis"},
+     { Group_Axis, Group_UAxis, "U-axis", group_is_available },
   #endif
   #ifdef V_AXIS
-     { Group_Axis, Group_VAxis, "V-axis"}
+     { Group_Axis, Group_VAxis, "V-axis", group_is_available }
   #endif
 #else
   #ifdef A_AXIS
-     { Group_Axis, Group_AAxis, "U-axis"},
+     { Group_Axis, Group_AAxis, "U-axis", group_is_available },
   #endif
   #ifdef B_AXIS
-     { Group_Axis, Group_BAxis, "V-axis"},
+     { Group_Axis, Group_BAxis, "V-axis", group_is_available },
   #endif
   #ifdef C_AXIS
-     { Group_Axis, Group_CAxis, "W-axis"},
+     { Group_Axis, Group_CAxis, "W-axis", group_is_available },
   #endif
 #endif
 };
@@ -420,6 +425,8 @@ static char axis_rate[8] = "mm/min";
 static char axis_accel[10] = "mm/sec^2";
 static char axis_steps[9] = "step/mm";
 
+#define AXIS_OPTS { .subgroups = On, .increment = 1 }
+
 PROGMEM static const setting_detail_t setting_detail[] = {
      { Setting_PulseMicroseconds, Group_Stepper, "Step pulse time", "microseconds", Format_Decimal, "#0.0", "2.0", NULL, Setting_IsLegacy, &settings.steppers.pulse_microseconds, NULL, NULL },
      { Setting_StepperIdleLockTime, Group_Stepper, "Step idle delay", "milliseconds", Format_Int16, "####0", NULL, "65535", Setting_IsLegacy, &settings.steppers.idle_lock_time, NULL, NULL },
@@ -532,14 +539,14 @@ PROGMEM static const setting_detail_t setting_detail[] = {
      { Setting_PositionIGain, Group_Spindle_Sync, "Spindle sync I-gain", NULL, Format_Decimal, "###0.000", NULL, NULL, Setting_IsExtended, &settings.position.pid.i_gain, NULL, is_group_available },
      { Setting_PositionDGain, Group_Spindle_Sync, "Spindle sync D-gain", NULL, Format_Decimal, "###0.000", NULL, NULL, Setting_IsExtended, &settings.position.pid.d_gain, NULL, is_group_available },
      { Setting_PositionIMaxError, Group_Spindle_Sync, "Spindle sync PID max I error", NULL, Format_Decimal, "###0.000", NULL, NULL, Setting_IsExtended, &settings.position.pid.i_max_error, NULL, is_group_available },
-     { Setting_AxisStepsPerMM, Group_Axis0, "?-axis travel resolution", axis_steps, Format_Decimal, "#####0.000", NULL, NULL, Setting_IsLegacyFn, set_axis_setting, get_float, NULL },
-     { Setting_AxisMaxRate, Group_Axis0, "?-axis maximum rate", axis_rate, Format_Decimal, "#####0.000", NULL, NULL, Setting_IsLegacyFn, set_axis_setting, get_float, NULL },
-     { Setting_AxisAcceleration, Group_Axis0, "?-axis acceleration", axis_accel, Format_Decimal, "#####0.000", NULL, NULL, Setting_IsLegacyFn, set_axis_setting, get_float, NULL },
-     { Setting_AxisMaxTravel, Group_Axis0, "?-axis maximum travel", axis_dist, Format_Decimal, "#####0.000", NULL, NULL, Setting_IsLegacyFn, set_axis_setting, get_float, NULL },
+     { Setting_AxisStepsPerMM, Group_Axis0, "-axis travel resolution", axis_steps, Format_Decimal, "#####0.000", NULL, NULL, Setting_IsLegacyFn, set_axis_setting, get_float, NULL, AXIS_OPTS },
+     { Setting_AxisMaxRate, Group_Axis0, "-axis maximum rate", axis_rate, Format_Decimal, "#####0.000", NULL, NULL, Setting_IsLegacyFn, set_axis_setting, get_float, NULL, AXIS_OPTS },
+     { Setting_AxisAcceleration, Group_Axis0, "-axis acceleration", axis_accel, Format_Decimal, "#####0.000", NULL, NULL, Setting_IsLegacyFn, set_axis_setting, get_float, NULL, AXIS_OPTS },
+     { Setting_AxisMaxTravel, Group_Axis0, "-axis maximum travel", axis_dist, Format_Decimal, "#####0.000", NULL, NULL, Setting_IsLegacyFn, set_axis_setting, get_float, NULL, AXIS_OPTS },
 #if ENABLE_BACKLASH_COMPENSATION
-     { Setting_AxisBacklash, Group_Axis0, "?-axis backlash compensation", axis_dist, Format_Decimal, "#####0.000", NULL, NULL, Setting_IsExtendedFn, set_axis_setting, get_float, NULL },
+     { Setting_AxisBacklash, Group_Axis0, "-axis backlash compensation", axis_dist, Format_Decimal, "#####0.000", NULL, NULL, Setting_IsExtendedFn, set_axis_setting, get_float, NULL, AXIS_OPTS },
 #endif
-     { Setting_AxisAutoSquareOffset, Group_Axis0, "?-axis dual axis offset", "mm", Format_Decimal, "-0.000", "-10", "10", Setting_IsExtendedFn, set_axis_setting, get_float, is_setting_available },
+     { Setting_AxisAutoSquareOffset, Group_Axis0, "-axis dual axis offset", "mm", Format_Decimal, "-0.000", "-10", "10", Setting_IsExtendedFn, set_axis_setting, get_float, is_setting_available, AXIS_OPTS },
      { Setting_SpindleAtSpeedTolerance, Group_Spindle, "Spindle at speed tolerance", "percent", Format_Decimal, "##0.0", NULL, NULL, Setting_IsExtended, &settings.spindle.at_speed_tolerance, NULL, is_setting_available },
      { Setting_ToolChangeMode, Group_Toolchange, "Tool change mode", NULL, Format_RadioButtons, "Normal,Manual touch off,Manual touch off @ G59.3,Automatic touch off @ G59.3,Ignore M6", NULL, NULL, Setting_IsExtendedFn, set_tool_change_mode, get_int, NULL },
      { Setting_ToolChangeProbingDistance, Group_Toolchange, "Tool change probing distance", "mm", Format_Decimal, "#####0.0", NULL, NULL, Setting_IsExtendedFn, set_tool_change_probing_distance, get_float, NULL },
@@ -1282,6 +1289,8 @@ inline static setting_id_t normalize_id (setting_id_t id)
         id -= id % AXIS_SETTINGS_INCREMENT;
     else if(id > Setting_EncoderSettingsBase && id <= Setting_EncoderSettingsMax)
         id = (setting_id_t)(Setting_EncoderSettingsBase + (id % ENCODER_SETTINGS_INCREMENT));
+    else if(id > Setting_ModbusTCPBase && id <= Setting_ModbusTCPMax)
+        id = (setting_id_t)(Setting_ModbusTCPBase + (id % MODBUS_TCP_SETTINGS_INCREMENT));
 
     return id;
 }
@@ -2071,21 +2080,21 @@ static bool is_group_available (const setting_detail_t *setting)
     return settings_is_group_available(setting->group);
 }
 
-bool settings_is_group_available (setting_group_t group)
+bool settings_is_group_available (setting_group_t id)
 {
-    bool available = false;
+    const setting_group_detail_t *group = setting_get_group_details(id);
 
-    switch(group) {
+    if(!group)
+        return false;
+
+    bool available = group->is_available ? group->is_available(group) : false;
+
+    if(!available) switch(group->id) {
 
         case Group_Probing:
             available = hal.probe.get_state != NULL;
             break;
 
-        case Group_Encoders:
-        case Group_Encoder0:
-            available = hal.encoder.get_n_encoders && hal.encoder.get_n_encoders() > 0;
-            break;
-
         case Group_Spindle_Sync:
             available = hal.driver_cap.spindle_sync;
             break;
@@ -2098,42 +2107,23 @@ bool settings_is_group_available (setting_group_t group)
             available = hal.stepper.get_ganged && hal.stepper.get_ganged(true).mask != 0;
             break;
 
-        case Group_General:
         case Group_Homing:
         case Group_Jogging:
         case Group_Limits:
         case Group_ControlSignals:
         case Group_Spindle:
-        case Group_Axis:
-        case Group_XAxis:
-        case Group_YAxis:
-        case Group_ZAxis:
-        #ifdef A_AXIS
-        case Group_AAxis:
-        #endif
-        #ifdef B_AXIS
-        case Group_BAxis:
-        #endif
-        #ifdef C_AXIS
-        case Group_CAxis:
-        #endif
-        #ifdef U_AXIS
-        case Group_UAxis:
-        #endif
-        #ifdef V_AXIS
-        case Group_VAxis:
-        #endif
             available = true;
             break;
 
         default:
             {
                 uint_fast16_t idx;
-                setting_details_t *details = settings_get_details();
+                setting_details_t *details = &setting_details;
+
                 do {
                     if(details->settings) {
                         for(idx = 0; idx < details->n_settings; idx++) {
-                            if(details->settings[idx].group == group && (available = is_available(&details->settings[idx])))
+                            if(details->settings[idx].group == id && (available = is_available(&details->settings[idx])))
                                 break;
                         }
                     }
@@ -2150,78 +2140,28 @@ setting_group_t settings_normalize_group (setting_group_t group)
     return (group > Group_Axis0 && group < Group_Axis0 + N_AXIS) ? Group_Axis0 : group;
 }
 
-/*
-setting_group_t settings_get_parent_group (setting_group_t group)
-{
-    uint_fast16_t idx;
-    setting_details_t *settings = settings_get_details();
-
-    for(idx = 0; idx < settings->n_groups; idx++) {
-        if(settings->groups[idx].id == group) {
-            group = settings->groups[idx].parent;
-            break;
-        }
-    }
-
-    return group;
-}
-*/
-
 bool settings_iterator (const setting_detail_t *setting, setting_output_ptr callback, void *data)
 {
     bool ok = false;
 
-    switch(setting->id) {
+    if(setting->group == Group_Axis0) {
 
-        case Setting_AxisStepsPerMM:
-        case Setting_AxisMaxRate:
-        case Setting_AxisAcceleration:
-        case Setting_AxisMaxTravel:
-        case Setting_AxisStepperCurrent:
-        case Setting_AxisMicroSteps:
-        case Setting_AxisBacklash:
-        case Setting_AxisAutoSquareOffset:
-        case Setting_AxisHomingFeedRate:
-        case Setting_AxisHomingSeekRate:
-        case Setting_AxisExtended0:
-        case Setting_AxisExtended1:
-        case Setting_AxisExtended2:
-        case Setting_AxisExtended3:
-        case Setting_AxisExtended4:
-        case Setting_AxisExtended5:
-        case Setting_AxisExtended6:
-        case Setting_AxisExtended7:
-        case Setting_AxisExtended8:
-        case Setting_AxisExtended9:
-            {
-                uint_fast8_t axis_idx = 0;
-                for(axis_idx = 0; axis_idx < N_AXIS; axis_idx++) {
+        uint_fast8_t axis_idx = 0;
+
+        for(axis_idx = 0; axis_idx < N_AXIS; axis_idx++) {
 #if N_AXIS > 3
-                    set_axis_setting_unit(setting, axis_idx);
+            set_axis_setting_unit(setting, axis_idx);
 #endif
-                    if(callback(setting, axis_idx, data))
-                        ok = true;
-                }
-            }
-            break;
-
-        case Setting_EncoderModeBase:
-        case Setting_EncoderCPRBase:
-        case Setting_EncoderCPDBase:
-        case Setting_EncoderDblClickWindowBase:
-            {
-                uint_fast8_t encoder_idx = 0, n_encoders = hal.encoder.get_n_encoders();
-                for(encoder_idx = 0; encoder_idx < n_encoders; encoder_idx++) {
-                    if(callback(setting, encoder_idx * ENCODER_SETTINGS_INCREMENT, data))
-                        ok = true;
-                }
-            }
-            break;
-
-        default:
-            ok = callback(setting, 0, data);
-            break;
-    }
+            if(callback(setting, axis_idx, data))
+                ok = true;
+        }
+    } else if(setting->flags.increment) {
+        setting_details_t *set;
+        setting = setting_get_details(setting->id, &set);
+        if(set->iterator)
+            ok = set->iterator(setting, callback, data);
+    } else
+        ok = callback(setting, 0, data);
 
     return ok;
 }
@@ -2240,7 +2180,7 @@ const setting_detail_t *setting_get_details (setting_id_t id, setting_details_t
                 if(details->settings[idx].group == Group_Axis0)
                     set_axis_setting_unit(&details->settings[idx], offset);
 #endif
-                if(offset && offset >= (details->settings[idx].group == Group_Encoder0 ? hal.encoder.get_n_encoders() : N_AXIS))
+                if(offset && details->iterator == NULL && offset >= (details->settings[idx].group == Group_Encoder0 ? hal.encoder.get_n_encoders() : N_AXIS))
                     return NULL;
                 if(set)
                     *set = details;
@@ -2298,6 +2238,15 @@ const setting_group_detail_t *setting_get_group_details (setting_group_t id)
     return detail;
 }
 
+/*
+setting_group_t setting_get_parent_group (setting_group_t id)
+{
+    const setting_group_detail_t *group = setting_get_group_details(id);
+
+    return group ? group->parent : Group_Unknown;
+}
+*/
+
 static status_code_t validate_value (const setting_detail_t *setting, float value)
 {
     float val;
diff --git a/settings.h b/settings.h
index 7ecdce6..eadad60 100644
--- a/settings.h
+++ b/settings.h
@@ -381,6 +381,12 @@ typedef enum {
     Setting_Panel_Encoder3_Cpd       = 559,
     Setting_Panel_SettingsMax        = 579,
 
+    Setting_ModbusTCPBase       = 600,    // Reserving settings values 600 to 639 for ModBus TCP (8 sets)
+    Setting_ModbusIpAddressBase = Setting_ModbusTCPBase + Setting_ModbusIpAddress,
+    Setting_ModbusPortBase      = Setting_ModbusTCPBase + Setting_ModbusPort,
+    Setting_ModbusIdBase        = Setting_ModbusTCPBase + Setting_ModbusId,
+    Setting_ModbusTCPMax        = 639,
+
     Setting_SettingsMax,
     Setting_SettingsAll = Setting_SettingsMax,
 
@@ -722,40 +728,49 @@ typedef enum {
     Group_Bluetooth,            //!< 17
     Group_AuxPorts,             //!< 18
     Group_ModBus,               //!< 19
-    Group_Encoders,             //!< 20
-    Group_Encoder0,             //!< 21
-    Group_Encoder1,             //!< 22
-    Group_Encoder2,             //!< 23
-    Group_Encoder3,             //!< 24
-    Group_Encoder4,             //!< 25
-    Group_UserSettings,         //!< 26
-    Group_Stepper,              //!< 27
-    Group_MotorDriver,          //!< 28
-    Group_VFD,                  //!< 29
-    Group_CANbus,               //!< 30
-    Group_Embroidery,           //!< 31
-    Group_Panel,                //!< 32
-    Group_Axis,                 //!< 33
+    Group_ModBusUnit0,          //!< 20
+    Group_ModBusUnit1,          //!< 21
+    Group_ModBusUnit2,          //!< 22
+    Group_ModBusUnit3,          //!< 23
+    Group_ModBusUnit4,          //!< 24
+    Group_ModBusUnit5,          //!< 25
+    Group_ModBusUnit6,          //!< 26
+    Group_ModBusUnit7,          //!< 27
+    Group_Encoders,             //!< 28
+    Group_Encoder0,             //!< 29
+    Group_Encoder1,             //!< 30
+    Group_Encoder2,             //!< 31
+    Group_Encoder3,             //!< 32
+    Group_Encoder4,             //!< 33
+    Group_UserSettings,         //!< 34
+    Group_Stepper,              //!< 35
+    Group_MotorDriver,          //!< 36
+    Group_VFD,                  //!< 37
+    Group_CANbus,               //!< 38
+    Group_Embroidery,           //!< 39
+    Group_Panel,                //!< 40
+    Group_Axis,                 //!< 41
 // NOTE: axis groups MUST be sequential AND last
-    Group_Axis0,                //!< 34
-    Group_XAxis = Group_Axis0,  //!< 35
-    Group_YAxis,                //!< 36
-    Group_ZAxis,                //!< 37
+    Group_Axis0,                //!< 42
+    Group_XAxis = Group_Axis0,  //!< 43
+    Group_YAxis,                //!< 44
+    Group_ZAxis,                //!< 45
 #ifdef A_AXIS
-    Group_AAxis,                //!< 38
+    Group_AAxis,                //!< 46
 #endif
 #ifdef B_AXIS
-    Group_BAxis,                //!< 39
+    Group_BAxis,                //!< 47
 #endif
 #ifdef C_AXIS
-    Group_CAxis,                //!< 40
+    Group_CAxis,                //!< 48
 #endif
 #ifdef U_AXIS
-    Group_UAxis,                //!< 41
+    Group_UAxis,                //!< 49
 #endif
 #ifdef V_AXIS
-    Group_VAxis,                //!< 42
+    Group_VAxis,                //!< 50
 #endif
+    Group_Unknown = 99,         //!< 99
     Group_All = Group_Root      //!< 0
 } setting_group_t;
 
@@ -775,10 +790,11 @@ typedef enum {
     Format_Int16,
 } setting_datatype_t;
 
-typedef struct {
+typedef struct setting_group_detail {
     setting_group_t parent;
     setting_group_t id;
     const char *name;
+    bool (*is_available)(const struct setting_group_detail *group);
 } setting_group_detail_t;
 
 typedef enum {
@@ -801,8 +817,10 @@ typedef union {
     uint8_t value;
     struct {
         uint8_t reboot_required :1,
-                allow_null: 1,
-                unused :6;
+                allow_null      :1,
+                subgroups       :1,
+                increment       :4,
+                unused          :1;
     };
 } setting_detail_flags_t;
 
@@ -854,6 +872,7 @@ typedef void (*settings_changed_ptr)(settings_t *settings, settings_changed_flag
 typedef void (*driver_settings_load_ptr)(void);
 typedef void (*driver_settings_save_ptr)(void);
 typedef void (*driver_settings_restore_ptr)(void);
+typedef bool (*driver_settings_iterator_ptr)(const setting_detail_t *setting, setting_output_ptr callback, void *data);
 
 typedef struct setting_details {
     const uint8_t n_groups;
@@ -870,6 +889,7 @@ typedef struct setting_details {
     driver_settings_save_ptr save;
     driver_settings_load_ptr load;
     driver_settings_restore_ptr restore;
+    driver_settings_iterator_ptr iterator;
 } setting_details_t;
 
 // NOTE: this must match the signature of on_get_settings in the setting_details_t structure above!