Modbus TCP Broadcaster

Owned by Gary Cane
Last updated: May 31, 2022


Operator Menu Location: Generic Hardware Operators Networking Modbus TCP


Operator Bitmap: 


Functional Description:

The Modbus TCP Broadcaster generic hardware operator provides access to a networking channel resource in the physical hardware. When the generic operator is linked to a specific networking hardware resource, it will broadcast a message over that channel resource using the Modbus TCP protocol.

The Modbus TCP Broadcaster operator has two inputs---the first, input x can be a structure, float or digital depending on the operator's Modbus Type and Data Type. Digital input b disables (HIGH) or enables broadcasting (LOW). If the digital input is not connected, broadcasting is always enabled.
The operator has two output pins. Pin Value is Out of Range is high when the data is saturated, meaning. Pin Comm Timeout determines when there is a network error.

User-Defined Properties:

Object Name

A string label that identifies the broadcast signal. It is used to associate this Modbus TCP Broadcast operator in one schema with Modbus TCP Receiver operator(s) in other schemas.

Modbus Type

This specifies the address space array, one of coil, discrete input, holding register or input register. An important concept is that an address for one Modbus Type is completely independent of the same address for a different Modbus Type. For example, Coil Address 15 bears no relationship whatsover to discrete Input address 15. They are completely independent spaces. This is true of all of the Modbus Type values.

Coil - the equivalent of a switch that has only two values, a one or a zero. Coils are both readable and writable.

Discrete Inputs - the equivalent of a switch that has only two values, a one or a zero. Coils are writable only by the module acting as a server, but readable by anyone.

Holding Registers - 16 bit integer values. Holding Registers are both readable and writeable.

Input Registers - 16 bit integer values. Input Registers are writable only by the module acting as a server, but readable by anyone.

Data Type

The Data Type is a configurable property of Holding Registers and Input registers describing how a 16 bit Holding Register or Input Register is to be formatted and interpreted.

Mapped Range

The 16 bit register is divided into 65536 (the number of unique equal value steps that can be expressed in 16 bits) discrete steps. Each step represents the (100% Mapping value minus the 0% Mapping value)/65536. For example, given a %100 Mapping value of 300 and a 0% mapping value of -10, each step has a value of 300-(-10)/65536 = 310/65536 = 0.004730224609, the Units per Step. When the floating point value on Broadcast Holding or Input operators pin is processed, it is first evaluated against the mapping range, in this example, -10 to 300. If it is -10 or less the number of steps is zero. It is clipped at the minimum for the range. If it is 300 or more the number of steps is 65535. It is clipped at the maximum for the range. If it falls within the range, the step count X = (Value - (0% Mapping Value))/Units per Step. For example, use a Value of 67.3. X = (67.3 - (-10))/0.004730224609 = 16341.71871. Because the step values are represented as integers, they are rounded up if the fractional part is 0.5 or greater or rounded down if < 0.5; therefore 16342 will be transmitted. The receiver processes it in reverse, as Value = (Steps * Units Per Steps)+(0% Mapping Value) = (16342 * 0.004730224609) + (-10) = 67.30133057. Note that this is not an error free conversion, the precision of the mapping operation is dictated by the range used; the smaller the range, the smaller the Units per Step value will be and greated the resolution possible. Use a range that is no larger than it need be.

Unsigned 16 bit - The floating point Value is rounded up or down to an integer (no fractional component) as a 16 bit unsigned number between 0 and 65535. A Value above or below this range is clipped to the minimum (0) or maximum (65535).

Signed 16 bit - The floating point Value is rounded up or down to an integer (no fractional component) as a 16 bit signed number between -32768 and 32767. A Value above or below this range is clipped to the minimum (-32768) or maximum (32767).

While not a part of the Modbus TCP standard, 32 bit, floating point and structures are supported between Chameleon nodes and some third party devices. These Data Types require multiple registers to represent each value.

Unsigned 32 bit - The floating point Value is rounded up or down to an integer (no fractional component) as a 32 bit unsigned number between 0 and 4,292,967,295. A Value above or below this range is clipped to the minimum (0) or maximum (4,292,967,295). It consumes two consecutive registers.

Signed 32 bit - The floating point Value is rounded up or down to an integer (no fractional component) as a 16 bit signed number between -2,147,483,648 and 2,147,483,647 . A Value above or below this range is clipped to the minimum (-2,147,483,648) or maximum (2,147,483,647). It consumes two consecutive registers.

Float - the floating point value (IEEE format) is transferred unaltered. It consumes two consecutive registers.

Structure - A structure may be a collection of boolean and floating point values. Each element of the structure, whether boolean or float, consumes two consecutive registers, with boolean structure members converted to and from floats. Structures are not likely to be supported on non-Chameleon hardware.

0% Mapping and 100% Mapping - the minimum and maximum range values used only when the Data Type (see above) is set to Mapped Range.

Timeout (Svrs>Poll Period)

If the Broadcaster is a server (is queried by a Modbus/TCP receiver located on another device or node) this value, in milliseconds, indicates a timeout period. If the broadcast operator is not regularly queried within the number of milliseconds provided, a timeout is presumed and the timeout pin will be made true until its receiver counterpart has queried it again.

Show Disable Broadcaster Pin

If checked, the pin used to disable broadcasts for this operator is visible.

Show Comm Timeout Pin

If checked, the pin used indicate transmission timeouts for this operator is visible.

Show Input Is Saturated Pin

If checked, the pin used to indicate that the value presented for broadcast exceeds the range for the Data Type selected.

Initial Value

The initial value to be broadcast.

Reorder
Because the use of multiple registers to represent 32 bit and floating point numbers is not standardized in Modbus TCP, it is left to the manufacturer how the registers should be ordered. To accommodate other manufacturers, a means to alter the register ordering is provided. Normally, the default of HH-HL-LH-LL will work correctly; this will use the first register for the highest order bits and the second register for the lowest order bits.


Comments: None.

See Also:
Modbus TCP Receiver