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 Settings	Net PHY Speed	Response Time [ms]
4800-8-1-E	1M	222
9600-8-1-E	1M	127
14400-8-1-E	1M	94
19200-8-1-E	1M	76
115200-8-1-E	2M	28
500000-8-1-E	2M	17

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:

State	LED Activity	LED Interval
Network Loss	Fast flash: 100ms on/off	500ms off
Network Sync	Continuous: 3sec on	500ms off
Network Wait	Slow 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.

Switch	Function	Description
SW1	Network start/config	On: Activate; Off: Default. See below.
SW2	Node mode	On: Master; Off: Slave.
SW3	RS485 parity enable	On: Enable parity; Off: Disable parity
SW4	RS485 parity mode	On: 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 #

Command	Response	Description
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 code	Write data packege size. up: uplink size; dn: downlink size
AT+LOG=x	Result code	Write Log enable level x: bit[0:2]. 3 levels
AT+ADDR=?	+ADDR=[xxyyxxyy]	Read net address. xxyyxxyy: address
AT+ADDR=[xxyyxxyy]	Result code	Write net address. xxyyxxyy: address. send`AT+SYSCMD=3`save config and send`AT+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=x	Result code	Send 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.