Upcoming changes

In the function determineNextEvent () the last target time will be the Period length added to calculate the next execution time. If the connection was interrupted for a long time, however, they accumulate many versions of the then with a shorter period length (tv_earliest_next_trigger_time) are processed. If the cycle times anyway are already tightly laid out, this can lead to an overload. Must be changed. The next execution time must be the current time plus Be cycle time.

Error Codes in Process Image

ModbusTCP

Modbus_Master_Status
16	0x10	Initialization is failed
17	0x11	This device is not readable(false IP, Cabel?)

Modbus_Action_Status
1	ILLEGAL FUNCTION	The applied function code is not allowed. Check whether the right function code is used.
2	ILLEGAL DATA ADDRESS	The applied address is not valid. The register is either read-only or not existed. Please check the address.
3	ILLEGAL DATA VALUE	At least one part of the applied data is invalid. It is possible that the count of register is exceed. Please check the value.
13	INVALID DATA	The Slave answered with an unknown package to me. This can occur, for example, after the connection has been interrupted. Please check your wiring.
104	CONNECTION RESET BY PEER	This is a TCP problem. It can occur if the addressed host has no instance of the modbus slave running.
110	CONNECTION TIMED OUT	The slave didn't respond in time or not at all. Please check your configuration and cabling.

ModbusRTU

Modbus_Master_Status
16	0x10	Initialization is failed
17	0x11	Serial connection can't be opened (wrong device name, invalid configuration)

Modbus_Action_Status
1	ILLEGAL FUNCTION	The applied function code is not allowed. Check whether the right function code is used.
2	ILLEGAL DATA ADDRESS	The applied address is not valid. The register is either read-only or not existed. Please check the address.
3	ILLEGAL DATA VALUE	At least one part of the applied data is invalid. It is possible that the count of register is exceed. Please check the value.
11	FAILED TO RESPOND	Resource temporarily unavailable. Usually means that the device is not present on the network.
12	INVALID CRC	A disturbed packet was received from the slave. This can occur, for example, after the connection has been interrupted. Please check your wiring.
13	INVALID DATA	An incomplete packet was received from the slave. This can occur, for example, after the connection has been interrupted. Please check your wiring.
110	CONNECTION TIMED OUT	The slave didn't respond in time or not at all. Please check your configuration and cabling.

All internal error messages that do not occur and do not need to be documented

ID
1	Illegal function
2	Illegal data address
3	Illegal data value
4	Slave device or server failure
5	Acknowledge
6	Slave device or server is busy
7	Negative acknowledge
8	Memory parity error
10	Gateway path unavailable
11	Target device failed to respond
12	Invalid CRC
13	Invalid data
14	Invalid exception code
15	Too many data

Example configuration for the config.rsc

Further information in document about configuration and I/O

{

    "config": {
        "modbusActions": [
            {
                "SlaveAddress" : 1,
                # Address of the Modbus slave which is addressed by the
                # command

                "FunctionCode" : 2,
                # Modbus function code see below

                "RegisterAddress" : 1,
                # Modbus register address (start address) of the slave

                "QuantityOfRegisters" : 8,
                # Number of Modbus registers that are written / read

                "ActionInterval" : 100000,
                # Time interval in which the command is sent from the
                # master in µsec. For the user, information in 1 ms
                # steps is sufficient

                "ProcessImageStartByte" : 2,
                # The offset in the Pi process image for the Modbus data

                "Action ID" : 1
                # Ascending ID for the command for information in the
                # event of an error
            },
            {
                "SlaveAddress" : 1,
                "FunctionCode" : 3,
                "RegisterAddress" : 1200,
                "QuantityOfRegisters" : 8,
                "ActionInterval" : 200000,
                "ProcessImageStartByte" : 18,
                "Action ID" : 2
            },
            {
                "SlaveAddress" : 2,
                "FunctionCode" : 16,
                "RegisterAddress" : 1024,
                "QuantityOfRegisters" : 8,
                "ActionInterval" : 500000,
                "ProcessImageStartByte" : 2,
                "Action ID" : 3
            }
        ]
    }
}

Modbus Function Codes:

Important function codes are marked with '*'.The other function codes may not need to be supported.

	Code	ID
*	eREAD_COILS	0x01
*	eREAD_DISCRETE_INPUTS	0x02
*	eREAD_HOLDING_REGISTERS	0x03
*	eREAD_INPUT_REGISTERS	0x04
*	eWRITE_SINGLE_COIL	0x05
*	eWRITE_SINGLE_REGISTER	0x06
	eREAD_EXCEPTION_STATUS	0x07
*	eWRITE_MULTIPLE_COILS	0x0F
*	eWRITE_MULTIPLE_REGISTERS	0x10
	eREPORT_SLAVE_ID	0x11
	eWRITE_MASK_REGISTER	0x16
	eWRITE_AND_READ_REGISTERS	0x17

Coils and Discrete Inputs are one bit in size. In the process image, however, one byte should be reserved for each bit.Holding registers and input registers have a size of 2 bytes.

For each Modbus command, an additional byte must be reserved in the Pi process image for error messages.

For the virtual device, a byte must also be reserved in the Pi process image for error messages.

For each Modbus command and the virtual device, a bit must be reserved to reset the error byte in the Pi process image

iluminat23 / revpi-modbus