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megaind-rpi

Modbus

The Industrial 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 megaind command.

Example:

~$ megaind 0 rs485wr 1 9600 1 0 1

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

~$ megaind -h rs485wr

display the full set of options

Slave Address

The slave address is add with the "stack level" jumpers. For example the jumpers configuration for stack level 1 (one jumper in position ID0) slave address offset to 1 corespond to slave address 2.

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
OPEN_DRAIN_1 0001 0x00
OPEN_DRAIN_2 0002 0x01
OPEN_DRAIN_3 0003 0x02
OPEN_DRAIN_4 0004 0x03
LED_1 0005 0x04
LED_2 0006 0x05
LED_3 0007 0x06
LED_4 0008 0x07
OPTO_RISING_COUNT_1 0009 0x08
OPTO_RISING_COUNT_2 0010 0x09
OPTO_RISING_COUNT_3 0011 0x0a
OPTO_RISING_COUNT_4 0012 0x0b
OPTO_FALLING_COUNT_1 0013 0x0c
OPTO_FALLING_COUNT_2 0014 0x0d
OPTO_FALLING_COUNT_3 0015 0x0e
OPTO_FALLING_COUNT_4 0016 0x0f

OPTO_RISING_COUNT coil enable/disable counting on rising edge of coresponding opto channel OPTO_FALLING_COUNT coil enable/disable counting on falling edge of coresponding opto channel

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
0-10V_IN_1 30001 0x00 mV
0-10V_IN_2 30002 0x01 mV
0-10V_IN_3 30003 0x02 mV
0-10V_IN_4 30004 0x03 mV
+/-10V_IN_1 30005 0x04 mV
+/-10V_IN_2 30006 0x05 mV
+/-10V_IN_3 30007 0x06 mV
+/-10V_IN_4 30008 0x07 mV
4-20mA_IN_1 30009 0x08 uA
4-20mA_IN_2 30010 0x09 uA
4-20mA_IN_3 30011 0x0a uA
4-20mA_IN_4 30012 0x0b uA
OPTO_COUNT_1 30013 0x0c
OPTO_COUNT_2 30014 0x0d
OPTO_COUNT_3 30015 0x0e
OPTO_COUNT_4 30016 0x0f

Holding registers

Access level Read/Write, Size 16 bits

Device function Register Address Modbus Address Measurement Unit Range
0-10V_OUT_1 40001 0x00 mV 0..10000
0-10V_OUT_2 40002 0x01 mV 0..10000
0-10V_OUT_3 40003 0x02 mV 0..10000
0-10V_OUT_4 40004 0x03 mV 0..10000
4-20mA_OUT_1 40005 0x04 uA 4000..20000
4-20mA_OUT_2 40006 0x05 uA 4000..20000
4-20mA_OUT_3 40007 0x06 uA 4000..20000
4-20mA_OUT_4 40008 0x07 uA 4000..20000
OPEN_DRAIN_PWM_1 40009 0x08 0..10000
OPEN_DRAIN_PWM_2 40010 0x09 0..10000
OPEN_DRAIN_PWM_3 40011 0x0a 0..10000
OPEN_DRAIN_PWM_4 40012 0x0b 0..10000

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)