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Modbus RTU Server v3.6.5

🚀 Production-Ready Arduino Mega 2560 Modbus RTU Server med Unified Prescaler Architecture, 3 Counter Modes (HW/SW/SW-ISR), CLI, og Timer Engine.

Version Platform Framework

📋 Indholdsfortegnelse

✨ Features

Modbus RTU Server

  • ✅ Full Modbus RTU slave implementering
  • ✅ Function codes: FC01, FC02, FC03, FC04, FC05, FC06, FC0F, FC10
  • ✅ RS-485 automatic direction control (pin 8)
  • ✅ Configurable slave ID (1-247 eller 0 for broadcast)
  • ✅ Configurable baudrate (300-115200 bps)
  • ✅ CRC16 validation
  • ✅ Automatic RTU frame gap timing

CLI (Command Line Interface)

  • ✅ Interactive Cisco-style shell over USB Serial
  • ✅ Remote echo & backspace support
  • ✅ Command history (3 commands, arrow key navigation)
  • ✅ 256 character command buffer
  • ✅ Case-insensitive commands
  • ✅ Aliases (sh, wr, rd, sv, ld, etc.)
  • ✅ Comprehensive help system

TimerEngine v2

  • ✅ 4 independent timers
  • ✅ Mode 1: One-shot sequences (3-phase)
  • ✅ Mode 2: Monostable (retriggerable)
  • ✅ Mode 3: Astable (blink/toggle)
  • ✅ Mode 4: Input-triggered (2 sub-modes)
  • ✅ Global status/control registers
  • ✅ EEPROM persistence

CounterEngine v7 (with v3.6.5 Unified Prescaler)

  • ✅ 4 independent counters with 3 operating modes
  • ✅ HW Mode (Timer5 ONLY): Direct hardware timer input on PIN 47 (PL2)
    • Highest precision, MAX ~20 kHz
    • CRITICAL FIX (v3.6.2): Timer5 uses PIN 47 (NOT pin 2!)
    • Only Timer5 routed to Arduino headers (Timer1/3/4 not available)
  • ✅ SW-ISR Mode: Interrupt-driven edge detection (INT0-INT5: pins 2,3,18,19,20,21)
    • Hardware interrupt triggered, deterministic
    • MAX ~20 kHz capable
    • NEW in v3.4.0, unified prescaler in v3.6.1, production ready
  • ✅ SW Mode: Software polling-based edge detection on GPIO pins
    • Flexible GPIO selection
    • Debounce filtering (1-255 ms)
    • MAX ~500 Hz (polling-limited)
    • Suitable for low-frequency signals
  • ✅ UNIFIED Prescaler Strategy (v3.6.0+) - BREAKING CHANGE
    • ALL modes count EVERY edge (no edge skipping)
    • Prescaler division ONLY at output (raw register)
    • Consistent behavior: HW, SW, SW-ISR identical
    • Prescaler values: 1, 4, 8, 16, 64, 256, 1024
  • ✅ Edge detection (rising/falling/both)
  • ✅ Direction (up/down)
  • ✅ BitWidth (8/16/32/64)
  • ✅ Float scale factor
  • ✅ Frequency measurement (0-20 kHz) with 1-2 sec timing windows
  • ✅ Separate raw register (counterValue / prescaler)
  • ✅ Consistent parameter naming (index-reg, raw-reg, freq-reg)
  • ✅ Automatic GPIO pin management for HW mode
  • ✅ Dynamic GPIO mappings display
  • ✅ Control register (reset/start/stop/reset-on-read)
  • ✅ Overflow detection & auto-reset
  • ✅ Auto-start on boot (configurable)
  • ✅ EEPROM persistence (schema v12)

EEPROM Configuration

  • ✅ Persistent configuration (schema v12 - GPIO persistence restored)
  • ✅ CRC checksum validation
  • ✅ Load/Save/Defaults commands
  • ✅ Modbus SAVE via FC06 (write reg 0 = 255)
  • ✅ Hostname persistence

GPIO Management

  • ✅ 54 digital pins available
  • ✅ Dynamic mapping (pin ↔ coil/input)
  • ✅ Static configuration persistence

🛠️ Hardware Setup

Board Configuration

  • Platform: Arduino Mega 2560 (ATmega2560 @ 16MHz)
  • RAM: 8 KB (83.0% used, 1.3 KB free) - increased due to v3.3.0 global config allocation
  • Flash: 256 KB (27.7% used) - plenty of headroom
  • EEPROM: 4 KB (schema v12)

Pin Assignments

Pin Function Description
0-1 USB Serial Debug/CLI (115200 baud)
18-19 Serial1 Modbus RTU (configurable baud)
8 RS-485 DIR Direction control for RS-485 transceiver
13 LED Heartbeat indicator
47 (PL2) HW Timer5 - ONLY IMPLEMENTED Timer5 external clock (HW counter mode) – v3.6.2 correct PIN
5, 6, 47 Timer1/3/4 pins (NOT ROUTED) Not available on Arduino headers
2, 3, 18, 19, 20, 21 INT0-INT5 External interrupts (SW-ISR counter mode)
2-53 GPIO Available for coils/inputs and SW counters

RS-485 Wiring

Arduino Pin RS-485 Module Function
18 (TX1) DI Data transmit
19 (RX1) RO Data receive
8 DE + RE Driver enable
VCC VCC 5V power
GND GND Ground

💿 Installation

Requirements

Quick Install

# Clone repository
git clone https://github.com/Jangreenlarsen/Modbus_server_slave.git
cd Modbus_server_slave

# Open in VS Code
code .

# Build
pio run

# Upload
pio run -t upload

# Monitor
pio device monitor

🚀 Quick Start

1. Upload Firmware

pio run -t upload

2. Open Serial Monitor

pio device monitor

3. Enter CLI Mode

Type CLI and press Enter to enter command mode.

4. Configure Counter - Three Operating Modes (v3.6.1)

Hardware Mode (Highest Precision, MAX ~20 kHz)

# Configure counter 1 in HARDWARE mode (Timer5 only on PIN 47)
set counter 1 mode 1 parameter hw-mode:hw-t5 \
  count-on:rising start-value:0 res:32 prescaler:1 \
  index-reg:100 raw-reg:104 freq-reg:108 \
  ctrl-reg:130 input-dis:125 direction:up scale:1.0

# Enable auto-start
set counter 1 start enable

Software-ISR Mode (Interrupt-Driven, MAX ~20 kHz)

# Configure counter 2 in SW-ISR mode (INT0 on pin 2)
set counter 2 mode 1 parameter hw-mode:sw-isr \
  count-on:rising start-value:0 res:32 prescaler:1 \
  index-reg:110 raw-reg:114 freq-reg:118 \
  ctrl-reg:131 input-dis:20 direction:up scale:1.0

# Map interrupt pin to discrete input (REQUIRED for SW-ISR!)
gpio map 2 input 20

# Enable auto-start
set counter 2 start enable

Software Polling Mode (Flexible GPIO, MAX ~500 Hz)

# Configure counter 3 in SOFTWARE mode (GPIO pin-based)
set counter 3 mode 1 parameter hw-mode:sw \
  count-on:rising start-value:0 res:32 prescaler:1 \
  index-reg:120 raw-reg:124 freq-reg:128 \
  ctrl-reg:132 input-dis:30 direction:up scale:2.5 \
  debounce:on debounce-ms:50

# Map GPIO pin 22 to discrete input 30
gpio map 22 input 30

# Enable auto-start
set counter 3 start enable
# Save all configuration
save

Counter Mode Selection:

  • hw-mode:hw-t5 - Timer5 on PIN 47 (PL2) - ONLY HW MODE IMPLEMENTED (v3.6.1+)
    • Timer1/3/4 NOT routed to Arduino headers (not available)
    • CRITICAL FIX v3.6.2: PIN 47, NOT pin 2!
  • hw-mode:sw-isr - Software-ISR on INT0-INT5 (pins 2,3,18,19,20,21) – MAX ~20 kHz
  • hw-mode:sw - Software polling on any GPIO pin – MAX ~500 Hz

BREAKING CHANGE (v3.6.0+):

  • ALL modes now count EVERY edge (no edge skipping)
  • Prescaler division happens ONLY at output (raw register)
  • Unified values: 1, 4, 8, 16, 64, 256, 1024

5. View Status

show counters
show config

📟 CLI Kommandoer

System Commands

show config              # Display full configuration
show version             # Show firmware version
save                     # Save config to EEPROM
load                     # Load config from EEPROM
defaults                 # Reset to factory defaults
reboot                   # Reboot system
set hostname <name>      # Set CLI hostname

Counter Commands (v3.3.0)

# Configure counter with HW/SW mode and all parameters
set counter <id> mode 1 parameter \
  hw-mode:<sw|hw-t1|hw-t3|hw-t4|hw-t5>  # NEW: Hardware/Software mode selection
  count-on:<rising|falling|both> \
  start-value:<n> \
  res:<8|16|32|64> \
  prescaler:<1..256> \
  index-reg:<reg>      # Scaled value register
  raw-reg:<reg>        # Raw unscaled register
  freq-reg:<reg>       # Frequency in Hz
  overload-reg:<reg>   # Overflow flag register
  ctrl-reg:<reg>       # Control register
  input-dis:<idx>      # Discrete input index (Modbus input mapping)
  direction:<up|down> \
  scale:<float> \
  debounce:<on|off> \
  debounce-ms:<ms>     # Debounce delay in ms (SW mode only)

# Counter control
set counter <id> start ENABLE|DISABLE        # Auto-start on boot
set counter <id> reset-on-read ENABLE|DISABLE
reset counter <id>                           # Reset to start value
clear counters                               # Reset all counters

# View status
show counters            # Show counter status with Hz column

Timer Commands

# Configure timer
set timer <id> mode <1|2|3|4> parameter \
  coil:<idx> P1:<high|low> P2:<high|low> \
  T1:<ms> T2:<ms> [T3:<ms>] \
  [trigger <di_idx> edge <rising|falling|both> sub <0|1>]

# Timer control
set timers status-reg:<n> control-reg:<n>
no set timer <id>        # Remove timer

# View status
show timers

GPIO Commands

gpio map <pin> coil <idx>     # Map pin to coil
gpio map <pin> input <idx>    # Map pin to input
gpio unmap <pin>              # Remove mapping
show gpio                     # Show all mappings

Modbus Commands

show regs [start] [count]     # Display holding registers
show coils                    # Display coil states
show inputs                   # Display input states
write reg <addr> <value>      # Write holding register
write coil <idx> <0|1>        # Write coil

🎯 Counter v3.3.0 Features

Hardware Mode (NEW in v3.3.0)

# Configure counter in HARDWARE mode (direct timer input)
set counter 1 mode 1 parameter hw-mode:hw-t1 \
  count-on:rising start-value:0 res:32 prescaler:1 \
  index-reg:100 raw-reg:104 freq-reg:108 \
  ctrl-reg:130 input-dis:125 direction:up scale:1.0

# View configuration with GPIO mapping
show config    # GPIO section shows: "gpio 5 DYNAMIC at input 125 (counter1 HW-T1)"
show counters  # pin column shows: "5" (hardware GPIO pin for Timer1)

Hardware Advantages:

  • Direct hardware timer input (no software overhead)
  • Accurate frequency measurement (0-20 kHz)
  • Fixed GPIO pins per timer (5, 47, 6, 46)
  • Automatic GPIO mapping (DYNAMIC)
  • Best for precision frequency measurement

Hardware Timer Mapping:

Timer GPIO Pin Input Type Use Case
T1 5 Input Capture Recommended for frequency
T3 47 Input Capture High precision counting
T4 6 Input Capture Parallel frequency measurement
T5 46 Input Capture Additional high-speed input

Software Mode (GPIO Pin-Based)

# Configure counter in SOFTWARE mode (GPIO-based edge detection)
set counter 2 mode 1 parameter hw-mode:sw \
  count-on:rising start-value:0 res:32 prescaler:1 \
  index-reg:110 raw-reg:114 freq-reg:118 \
  ctrl-reg:131 input-dis:20 direction:up scale:2.5 \
  debounce:on debounce-ms:50

# Map GPIO pin to discrete input (required for SW mode)
gpio map 22 input 20

# View configuration
show config    # GPIO section shows: "gpio 22 at input 20"
show counters  # pin column shows: "22" (mapped GPIO pin)

Software Advantages:

  • Flexible GPIO pin selection (any digital pin)
  • Prescaler and debounce filtering
  • Discrete input mapping (via gpio map command)
  • Suitable for slow signals or variable mapping

Software Limitations:

  • Software-based edge detection (less precise)
  • Cannot use hardware timer inputs
  • Prescaler only available in software mode

Frequency Measurement

# Automatic frequency measurement (HW or SW mode)
# Updated every second with validation
set counter 1 mode 1 parameter \
  hw-mode:hw-t1 count-on:rising res:32 \
  index-reg:100 freq-reg:108 input-dis:125

# Read via Modbus FC04 (Read Input Registers)
read reg 100   # Scaled counter value
read reg 108   # Frequency in Hz (0-20000)

Frequency Features:

  • Automatic Hz measurement every second
  • Timing window validation (1-2 sec)
  • Delta count validation (max 100kHz)
  • Overflow wrap-around detection
  • Result clamping (0-20000 Hz)
  • Stable under Modbus bus activity
  • Auto-reset on counter overflow

Frequency Algorithm:

  1. Measure count delta over 1-2 second window
  2. Validate delta against max 100kHz threshold
  3. Detect overflow wrap-around
  4. Calculate: Hz = (delta_count × prescaler) / window_seconds
  5. Clamp result to 0-20000 Hz range
  6. Reset on counter reset, overflow, or 5-sec timeout

Raw Register

# Separate scaled and raw value registers
set counter 1 mode 1 parameter \
  index-reg:100 raw-reg:104 scale:2.5

# Read via Modbus
read reg 100   # Scaled value: counterValue × 2.5
read reg 104   # Raw value: actual counter value

Use Cases:

  • index-reg: Application-specific scaled values (temperature, flow, etc.)
  • raw-reg: Diagnostics and debugging
  • Both updated simultaneously

Consistent Naming

Parameter names (v3.3.0 - backward compatible):

  • hw-mode = operation mode (NEW: sw, hw-t1, hw-t3, hw-t4, hw-t5)
  • index-reg = scaled value register
  • raw-reg = raw unscaled register
  • freq-reg = frequency in Hz
  • overload-reg = overflow flag register
  • ctrl-reg = control bits register
  • input-dis = discrete input index (Modbus mapping)

Legacy names still work:

  • reg → index-reg
  • count-reg → index-reg
  • control-reg → ctrl-reg
  • input → input-dis

GPIO Mapping Reference

# View all GPIO mappings (including DYNAMIC HW counter mappings)
show config

# Example output for HW counter 1 on Timer1:
# GPIO Mappings:
#   gpio 5 DYNAMIC at input 125 (counter1 HW-T1)
#
# For SW counter 2 on pin 22:
#   gpio 22 at input 20

# Manually map GPIO pin to discrete input (SW mode)
gpio map 22 input 20
gpio map 25 input 21
gpio unmap 22

# Map GPIO pin to coil
gpio map 30 coil 10
gpio unmap 30

GPIO Mapping Rules:

  • HW Mode: GPIO pins are automatic (5, 47, 6, 46 for T1, T3, T4, T5)
  • SW Mode: User must map GPIO pin via gpio map <pin> input <idx>
  • One GPIO pin can only map to one input or coil
  • GPIO mappings are persistent (saved in EEPROM)

⏱️ Timer Features

Mode 1: One-shot

set timer 1 mode 1 parameter \
  coil:10 P1:high P2:low P3:low \
  T1 1000 T2 500 T3 0

Mode 3: Astable (Blink)

set timer 2 mode 3 parameter \
  coil:11 P1:high P2:low \
  T1 500 T2 500

Mode 4: Input-triggered

# Single-phase pulse (retrigger after T1)
set timer 3 mode 4 parameter \
  coil:15 P1:high P2:low T1 200 \
  trigger 12 edge rising sub 0

# Two-phase sequence (retrigger after T1+T2)
set timer 4 mode 4 parameter \
  coil:16 P1:high P2:low T1 200 T2 300 \
  trigger 13 edge rising sub 1

📚 Dokumentation

Manualer (v3.6.5)

  • Modbus server V3.6.5 Manual - Complete System Reference.html - ✨ LATEST Complete HTML manual with all v3.6.5 features

    • v3.6.5: Slave ID persistence fix, Baudrate sync improvements
    • Counter frequency limitations documented: HW/ISR ~20kHz, SW ~500Hz
    • Unified prescaler architecture (v3.6.0-v3.6.1)
    • All 3 counter modes: HW, SW, SW-ISR (v3.3.0 foundation + v3.6.5 complete)
    • ATmega2560 hardware limitation documentation (v3.4.7 discovery)
    • BREAKING CHANGES documentation
    • Interactive CLI command reference
    • Frequency measurement with prescaler
    • Practical examples with all 3 modes
    • Complete troubleshooting guide

  • MANUAL.md - Komplet Markdown manual v3.3.0 (dansk/english)

    • Hardware/Software counter modes
    • GPIO mapping and DYNAMIC configuration
    • CLI kommando reference med eksempler
    • Frequency measurement og timer features
    • Extensive troubleshooting section

Guides

📊 Version Info

Version:        v3.6.5
Build Date:     2025-11-15
EEPROM Schema:  v12
Platform:       Arduino Mega 2560 (ATmega2560 @ 16MHz)
Framework:      Arduino + PlatformIO
RAM Usage:      83.0% (6798 / 8192 bytes) - 1.3 KB free
Flash Usage:    27.7% (70226 / 253952 bytes) - good headroom
Status:         ✅ PRODUCTION READY (Complete with Slave ID Persistence Fix)

v3.6.5 Highlights (2025-11-15) - Slave ID Persistence & Frequency Documentation

  • 🔴 CRITICAL BUGFIX: Slave ID and Baudrate Persistence
    • set id and set baud commands now sync globalConfig immediately
    • Prevents accidental revert if configApply() called later
    • User must still run save to persist to EEPROM
  • 📊 DOCUMENTATION: Counter Frequency Limitations
    • HW (Timer5 only): MAX ~20 kHz input frequency
    • SW-ISR (INT0-INT5): MAX ~20 kHz input frequency
    • SW (Polling): MAX ~500 Hz input frequency (main loop overhead)
  • ✅ Cleaned Debug Output – removed verbose boot messages
  • 📝 Updated HTML Manual – added frequency limitations table and Timer5 PIN documentation

v3.6.1 Highlights (2025-11-14) - Unified Prescaler Architecture Complete

  • 🔴 CRITICAL FIX: SW-ISR mode prescaler consistency
    • Removed edge-skipping from interrupt handler
    • NOW: ALL three modes (HW, SW, SW-ISR) count EVERY edge
    • Prescaler division happens ONLY at output (raw register)
    • Complete consistency across all counter modes
  • ✅ Unified Prescaler Strategy (v3.6.0-v3.6.1)
    • HW mode: Hardware counts all pulses → raw = value / prescaler
    • SW mode: Software counts all edges → raw = value / prescaler
    • SW-ISR mode: ISR counts all edges → raw = value / prescaler
    • Prescaler values: 1, 4, 8, 16, 64, 256, 1024
  • ✅ SW-ISR Mode Production Ready
    • Interrupt-driven edge detection (INT0-INT5: pins 2,3,18,19,20,21)
    • Deterministic, 5-20 kHz capable
    • Fully integrated with unified prescaler architecture
  • ⚠️ BREAKING CHANGE: SW/SW-ISR counters will show different values after upgrade

v3.6.0 Highlights (2025-11-14) - CRITICAL: SW Mode Prescaler Fix

  • 🔴 CRITICAL FIX: SW mode prescaler consistency with HW mode
    • Removed edgeCount prescaler check (was double-counting)
    • ALL modes now count EVERY edge (no edge skipping)
    • Prescaler division happens ONLY at output
    • Unified behavior: HW, SW, SW-ISR identical
  • 💡 Discovery: ATmega2560 Hardware Limitation (v3.4.7)
    • External clock mode CANNOT use hardware prescaler
    • Solution: 100% software prescaler implementation

v3.4.7 Highlights (2025-11-14) - Software Prescaler Implementation

  • 🔍 ROOT CAUSE DISCOVERED: ATmega2560 Timer5 hardware limitation
    • External clock (0x07): Counts pulses, no prescaler available
    • Internal prescaler (0x02-0x05): Count 16MHz system clock, ignore pulses!
    • Solution: Hardware ALWAYS uses external clock mode
    • Prescaler implemented 100% in software

v3.4.3 Highlights (2025-11-13) - Timer5 Pin Mapping Fix

  • 🔴 CRITICAL: Timer5 uses pin 2 (NOT pin 46!)
    • Verified working with hardware testing
    • Updated all documentation

Version History (Selection)

Version Date Key Features
v3.6.5 2025-11-15 🔴 Slave ID/Baud persistence fix, Counter frequency limitations documented, clean debug output
v3.6.3 2025-11-15 🔴 reset-on-read HW fix, frequency DOWN direction fix, show config improvements
v3.6.1 2025-11-14 🔴 SW-ISR prescaler fix, unified architecture, SW-ISR production ready
v3.6.0 2025-11-14 🔴 CRITICAL: SW mode prescaler fix, unified strategy
v3.5.0 2025-11-14 Show counters display bug fix
v3.4.7 2025-11-14 🔴 Software prescaler implementation, ATmega2560 limitation discovered
v3.4.3 2025-11-13 🔴 Timer5 pin correction (PIN 47, not pin 2)
v3.4.0 2025-11-13 SW-ISR interrupt mode production ready
v3.3.0 2025-11-11 Hardware counter mode, HW/SW dual modes, GPIO management
v3.2.0 2025-11-10 Frequency measurement, raw register, consistent naming
v3.1.9 2025-11-09 Counter control improvements, CLI enhancements

🤝 Contributing

Contributions are welcome! Please:

  1. Fork the repository
  2. Create a feature branch
  3. Submit a pull request

📞 Support

📄 License

This project is open source. Check repository for license details.

🎉 Acknowledgments

Built with:

Status: PRODUCTION READY ✅

Last updated: 2025-11-15 | v3.6.5 - Slave ID Persistence Fix & Frequency Documentation

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