Skip to content

Latest commit

 

History

History
65 lines (45 loc) · 1.84 KB

MODBUS.md

File metadata and controls

65 lines (45 loc) · 1.84 KB
Raw

3relind-rpi

Modbus

The Three 40A/240V Relays RS485 Daisy-chainable HAT for Raspberry Pi can be accessed thru Modbus RTU protocol over RS-485 port. You can set-up the RS-485 port with 3relind command.

Example:

~$ 3relind 0 cfg485wr 1 9600 1 0 1

Set Modbus RTU , Baudrate: 9600bps, 1 Stop Bit, parity: None, slave address base: 1

~$ 3relind -h rs485wr

display the full set of options

Slave Address

The five address switches have a dual purpose. When the card is accessed from Raspberry Pi, the switches define the offset of the I2C address, permitting changing the adress to avoid adress conflict on the bus. When the card is accessed through MODBUS protocol over the RS485 port, the switches define the offset of the RS485 base address set by the software.

Modbus object types

All modbus RTU object type with standard addresses are implemented : Coils, Discrete Inputs, Input registers, Holding registers.

Coils

Acces level Read/Write, Size 1 bit

Device function Register Address Modbus Address
COIL_RELAY1 0001 0x00
COIL_RELAY2 0002 0x01
COIL_RELAY3 0003 0x02

Discrete Inputs

NONE

Input registers

Access level Read Only, Size 16 bits

Device function Register Address Modbus Address Measurement Unit
IR_TEMP 30001 0x00 C

Holding registers

Access level Read/Write, Size 16 bits

NONE

Function codes implemented

  • Read Coils (0x01)
  • Read Discrete Inputs (0x02)
  • Read Holding Registers (0x03)
  • Read Input Registers (0x04)
  • Write Single Coil (0x05)
  • Write Single Register (0x06)
  • Write Multiple Coils (0x0f)
  • Write Multiple registers (0x10)