Modbus Server
The Modbus Protocol is a messaging structure. It is used to establish master-slave/client-server communication between intelligent devices. It is a de facto standard. The Modbus RTU specification defines the default communication protocol over serial lines. The Modbus TCP/IP specification takes the Modbus instruction set and wraps TCP/IP around it.
HSYCO’s MODBUS TCP SERVER I/O Server implements a Modbus TCP/IP server, allowing external Modbus clients to connect to HSYCO and perform any standard Modbus function.
This support is implemented as a simple Java API.
Contents
HSYCO Configuration
Options
ID | Default | Values | Description |
---|---|---|---|
eventslog | false | true | if the general eventsLog option is also true in hsyco.ini, Modbus events for this gateway are written in the log files |
false | Modbus events for this gateway are not written in the log files, even if the eventsLog option is true in hsyco.ini |
Modbus Server Integration
The Modbus TCP Server is implemented as a multi-threaded socket server that can accept multiple concurrent connections.
There are no hard-coded limits to the number of concurrent connections and no idle time-out mechanism to disconnect connections that don’t do any traffic for a certain amount of time. A socket-level keepalive mechanism is in place to ensure that a socket thread is closed and resources freed if the client drops the connection without a graceful close.
It is the clients’ responsibility to ensure the correct handling of connections to the server.
Whenever a client sends a Modbus request to the HSYCO server, the Modbus TCP Server will execute a Java callback method passing the complete PDU as a byte array, and respond with a PDU based on the returned byte array or, if the callback method is not defined or returns null, it will execute the Modbus read or write function using its internal data tables.
Datapoints
The naming convention HSYCO uses for the events is closely related to the Modbus addressing standards and data types.
The data point names always begin with the same format: <ioserver_id>.unitid.address, where unitid is the Modbus slave device address, from 1 to 247, and address is the initial register address you are reading.
The supported public function codes are:
- 01: Read Coils
- 02: Read Discrete Inputs
- 03: Read Holding Registers
- 04: Read Input Registers
- 05: Write Single Coil
- 06: Write Single Register
- 15: Write Multiple Coils
- 16: Write Multiple Registers
- 22: Mask Write Register
These functions read and write data on four distinct data tables:
Table | Suffix | Object Type | Mode | Functions |
---|---|---|---|---|
Discrete Inputs | .di | Single bit | Read Only | 02 |
Coils | .co | Single bit | Read Write | 01 05 15 |
Input Registers | .ir | 16-bit word | Read Only | 04 |
Holding Registers | .hr | 16-bit word | Read Write | 03 06 16 22 |
Operations on Input Registers and Holding Registers tables support the following data types:
Type code | Description | Return range | Number of registers |
---|---|---|---|
ushort | unsigned short integer | 0 ... 65535 | 1 |
uint | unsigned integer | 0 ... (232 - 1) | 2 |
ulong | unsigned long integer | 0 ... (264 - 1) | 4 |
short signed | short integer | -32768 ... +32767 | 1 |
int | signed integer | -231 ... (231 - 1) | 2 |
long | signed long integer | -263 ... (263 - 1) | 4 |
float | signed IEEE 754 floating point | +/- 2-149 ... (2-2-23)x2127 | 2 |
Discrete Inputs Data Table
The internal discrete inputs data table can be read by a Modbus client, and written locally to set the discrete inputs’ values.
ID | Value | R/W | Description |
---|---|---|---|
unitid.address.di | bit:0 bit:false bit:off |
W | sets a single bit in the discrete inputs data table to off |
bit:1 bit:true bit:on |
W | sets a single bit in the discrete inputs data table to on | |
bits:<0|1|-...> '-' characters in the sequence are skipped |
W | sets multiple bits in the discrete inputs data table. The left-most bit in the sequence is the discrete input at <address> |
Coils Data Table
The internal coils data table can be read or written by a Modbus client, and written locally to set the coils’ values.
ID | Value | R/W | Description |
---|---|---|---|
unitid.address.co | bit:0 bit:false bit:off |
W | sets a single coil in the coils data table to off |
bit:1 bit:true bit:on |
W | sets a single coil in the coils data table to on | |
bits:<0|1|-...> '-' characters in the sequence are skipped |
W | sets multiple coils in the coils data table. The left-most bit in the sequence is the coil at <address> | |
subscribe | W | subscribes one coil at <address> for event notification | |
subscribe:<n> | W | subscribes <n> consecutive coils starting at <address> for event notification | |
0 1 |
R | the status of the coil at <address>. Events are generated, only for coils that have been subscribed, when the coil is written by a Modbus client, even if there is no change of value |
The <n> value after subscribecoils: can also be a variable, that will be replaced with its numeric content.
Input Registers Data Table
The internal input registers data table can be read by a Modbus client, and written locally to set the registers’ values.
ID | Value | R/W | Description |
---|---|---|---|
unitid.address.ir | ushort:<value> | W | writes an unsigned short number to the input registers table |
uint:<value> | W | writes an unsigned integer number to the input registers table | |
ulong:<value> | W | writes an unsigned long number to the input registers table | |
short:<value> | W | writes a signed short number to the input registers table | |
int:<value> | W | writes a signed integer number to the input registers table | |
long:<value> | W | writes a signed long number to the input registers table | |
float:<value> | W | writes a floating-point number using the IEEE Standard 754 representation to the input registers table | |
hex:<value> | W | writes raw hex bytes to the input registers table | |
bits:<0|1|-...> '-' characters in the sequence are skipped |
W | writes 16 bits to a single register in the input registers table. The leftmost bit is the MSB |
Holding Registers Data Table
The internal holding registers data table can be read or written by a Modbus client, and written locally to set the registers’ values.
ID | Value | R/W | Description |
---|---|---|---|
unitid.address.hr | ushort:<value> | W | writes an unsigned short number to the holding registers table |
uint:<value> | W | writes an unsigned integer number to the holding registers table | |
ulong:<value> | W | writes an unsigned long number to the holding registers table | |
short:<value> | W | writes a signed short number to the holding registers table | |
int:<value> | W | writes a signed integer number to the holding registers table | |
long:<value> | W | writes a signed long number to the holding registers table | |
float:<value> | W | writes a floating-point number using the IEEE Standard 754 representation to the holding registers table | |
hex:<value> | W | writes raw hex bytes to the holding registers table | |
bits:<0|1|-...> '-' characters in the sequence are skipped |
W | writes 16 bits to a single register in the holding registers table. The leftmost bit is the MSB | |
subscribe:ushort | W | subscribes an unsigned short at <address> for event notification | |
subscribe:uint | W | subscribes an unsigned int starting at <address> for event notification | |
subscribe:ulong | W | subscribes an unsigned long starting at <address> for event notification | |
subscribe:short | W | subscribes a signed short integer at <address> for event notification | |
subscribe:int | W | subscribes a signed int starting at <address> for event notification | |
subscribe:long | W | subscribes a signed long starting at <address> for event notification | |
subscribe:float | W | subscribes a floating-point number using the IEEE Standard 754 representation starting at <address> for event notification | |
subscribe:hex | W | subscribes a single register at <address> for event notification using the hex notation | |
subscribe:bits | W | subscribes the 16 individual bits of a single register at <address> for event notification | |
data type value | R | the decimal or hexadecimal value of the data type at <address>. Events are generated, based on subscribed data types and addresses, when the data is written by a Modbus client, even if there is no change of value | |
unitid.address.hr.<n> <n> from 1 to 16; <n>=1 is the LSB of first byte; <n>=8 is MSB of first byte; <n>=9 is LSB of second byte; <n>=16 is MSB of second byte |
0 or 1 bit value | R | the individual bits of a holding register at <address>. Events are generated, for bits subscriptions only, when the data is written by a Modbus client, even if there is no change of value |
Java Callback Methods API
ModbusEvent
static byte[] ModbusEvent(String name, String InetAddress addr, int unitid, byte[] pdu)
This event is triggered by any valid Modbus request from a client connected to the IP address and port of the HSYCO’s Modbus server, and can override the default server’s response.
This method should return a valid PDU, that will be sent back to the client. If the method returns null, the server will perform the Modbus function on its internal data tables.
Parameters:
- name - the I/O Server name
- addr - the client’s address
- unitid - the Modbus unit id set in the client’s request
- pdu - the full PDU byte array, starting with the function code.