Wireless Modbus Module

Introduction to the Wireless Modbus Module #

Overview of the Modbus Protocol #

Modbus is an application-layer messaging protocol, designed in 1979 by Modicon, which facilitates master/slave interaction between devices. A de facto communication standard in industrial electronics, it has the following features:

  • Master-Slave Architecture: One master device issues commands to one or more slave devices that respond in kind.
  • Data Representation: Modbus categorizes data as either coils (binary) or registers (numeric), offering diverse data manipulation capabilities.
  • Variants: Modbus has adapted to different environments with variants like Modbus RTU, Modbus ASCII, and Modbus TCP/IP.

The RS485 Communication Standard #

RS485, or EIA-485, prescribes electrical specifications for drivers and receivers in digital multipoint systems. It is characterized by:

  • Extended Communication Range: Capable of transmitting data up to 4000 feet (~1200 meters).
  • Noise Resistance: Differential signaling provides robustness against voltage fluctuations and electromagnetic interference.
  • Multi-Drop Configurations: Supports up to 32 devices on a single bus network.

RS485’s reliability is a cornerstone of industrial controls in leveraging Modbus protocol.

Connection #

RS485 Connection #

A standard RS485 wiring diagram depicting a “daisy-chain” topology is shown:

RS485 Connection

Connection of the Wireless Modbus #

Replacement of wired RS485 connections with a wireless module:

WM Connection

Features of the Wireless Modbus Module #

Firmware version 0.2

The module supports baud rates [in bps]: 1200 to 1000000, including automatic master node baud rate detection and synchronization.

Communication Between Master and Slave #

The interaction comprises the master’s request, the slave’s response, and the corresponding response times as shown:

Request Response

Example timing for a 69-byte request and 8-byte response Modbus RTU query. Response timing across UART and wireless PHY settings:

UART SettingsNet PHY SpeedResponse Time [ms]
4800-8-1-E1M222
9600-8-1-E1M127
14400-8-1-E1M94
19200-8-1-E1M76
115200-8-1-E2M28
500000-8-1-E2M17

Configurations and User Interface #

Configuration channels include ATCMD, UART-based commands, physical interfacing (buttons/switches), and upcoming BLE.

LED Indicators #

Two LEDs (Blue and Red) denote operational states. Patterns of their light signify network status and the network node mode. It varies as follows - fast flash, slow flash, and constant on. For example:

StateLED ActivityLED Interval
Network LossFast flash: 100ms on/off500ms off
Network SyncContinuous: 3sec on500ms off
Network WaitSlow flash(500ms on/off)500ms off

LED Timing

Dip Switch Configuration #

Settings like SW1 and SW2 determine network status and node mode, respectively.

Setting RS485 parity with SW3 and SW4.

SwitchFunctionDescription
SW1Network start/configOn: Activate; Off: Default. See below.
SW2Node modeOn: Master; Off: Slave.
SW3RS485 parity enableOn: Enable parity; Off: Disable parity
SW4RS485 parity modeOn: ODD Parity; Off: EVEN parity

SW1 Configuration Details

  • ON to OFF: Trigger reconfiguration; a fast flash indicates readiness to reconfigure.

SW Config LED

AT Commands #

Each command starts with AT and ends with a terminator. The command and response bodies vary by read parameter or result code.

Normal AT Commands #

CommandResponseDescription
AT+MODE=?,+MODE=[m,1,0]Read the device Mode. m: 1, master; 0, slave.
AT+STATE=?,+STATE=[x,p,ch]Read net state. x:1, sync; 0, loss. p: phy. ch：channels
AT+UART=?+UART=[baud,data,stop,parity,th]Read RS485 UART setting. baud:baudrate; data:data bits(8); stop: stop bits(0: 1bit, 1: 2bits), parity:(0:disable, 1: odd, 2: even); th: internal threshold.
AT+PKTL=?,+PKTL=[up,dn]Read data packege size. up: uplink size; dn: downlink size
AT+PKTL=[up,dn],Result codeWrite data packege size. up: uplink size; dn: downlink size
AT+LOG=xResult codeWrite Log enable level x: bit[0:2]. 3 levels
AT+ADDR=?+ADDR=[xxyyxxyy]Read net address. xxyyxxyy: address
AT+ADDR=[xxyyxxyy]Result codeWrite net address. xxyyxxyy: address. sendAT+SYSCMD=3save config and sendAT+SYSCMD=1 to apply
AT+VER=?+VER=[xxH]Read firmware version
AT+NET=?+NET=[p,t,d,u]Read net information. p:phy, t: type, d:downlink length; u:uplink length
AT+SYSCMD=xResult codeSend system command. x: 1, reset; 2, restore; 3, save config.

Responses follow the <CR><LF> structure.

Result Codes #

Result codes for command outcomes:

  • 0 for success,
  • 0x1001 for Command execution error
  • 0x100A for Bad command
  • 0x100B for Bad format
  • 0x100D for Bad parameter
  • 0x100E for Overtime
  • Others for Protocol stack error

Advanced Commands #

There are also advanced commands for specialized tasks.

For detailed information, consult the Engineer’s Manual.