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megaioind-rpi

Modbus

The Industrial and Building Automation I/O Expansion cards for Raspberry Pi can be accessed thru Modbus RTU protocol over RS-485 port. You can set-up the RS-485 port with megaioind command.

Example:

~$ megaioind 0 wcfgmb 1 9600 0 0

Set Modbus RTU , Baudrate: 9600bps, parity: None. 1 Stop Bit,

~$ megaioind -h wcfgmb

display the full set of options

Slave Address

The slave address is set with the "stack level" jumpers. For example the jumpers configuration for stack level 0 (all jumpers removed) corespond to slave address 1.

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
RELAY_1 0001 0x00
RELAY_2 0002 0x01
RELAY_3 0003 0x02
RELAY_4 0004 0x03
OPEN_COLLECTOR_1 0005 0x04
OPEN_COLLECTOR_2 0006 0x05
OPEN_COLLECTOR_3 0007 0x06
OPEN_COLLECTOR_4 0008 0x07

Discrete Inputs

Access level Read Only, Size 1 bit

Device function Register Address Modbus Address
OPTO_1 10001 0x00
OPTO_2 10002 0x01
OPTO_3 10003 0x02
OPTO_4 10004 0x03

Input registers

Access level Read Only, Size 16 bits

Device function Register Address Modbus Address Measurement Unit
4-20mA_IN_1 30001 0x00 uA
4-20mA_IN_2 30002 0x01 uA
4-20mA_IN_3 30003 0x02 uA
4-20mA_IN_4 30004 0x03 uA
0-10V_IN_1 30005 0x04 mV
0-10V_IN_2 30006 0x05 mV
0-10V_IN_3 30007 0x06 mV
0-10V_IN_4 30008 0x07 mV
10K_R_IN_1 30009 0x08 ohm
10K_R_IN_2 30010 0x09 ohm
10K_R_IN_3 30011 0x0a ohm
10K_R_IN_4 30012 0x0b ohm

Holding registers

Access level Read/Write, Size 16 bits

Device function Register Address Modbus Address Measurement Unit
4-20mA_OUT_1 40001 0x00 uA
4-20mA_OUT_2 40002 0x01 uA
4-20mA_OUT_3 40003 0x02 uA
4-20mA_OUT_4 40004 0x03 uA
0-10V_OUT_1 40005 0x04 mV
0-10V_OUT_2 40006 0x05 mV
0-10V_OUT_3 40007 0x06 mV
0-10V_OUT_4 40008 0x07 mV
0-10V_OUT_5 40009 0x08 mV
0-10V_OUT_6 40010 0x09 mV
0-10V_OUT_7 40011 0x0a mV
0-10V_OUT_8 40012 0x0b mV

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)