Modbus Register Receiver

Operator Menu Location: Generic Hardware Operators

Networking

Modbus

Operator Bitmap:

Functional Description:
The Modbus Register Receiver 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 receive messages broadcast over that channel resource using the Modbus protocol.

The Modbus Register Receiver operator decodes Modbus messages broadcasted over a network. The operator has three outputs:
• Analog output

is the value of the broadcast signal obtained from the network.
•Output

indicates if the value has changed since the last transmission. In order for the operator to declare a change in value, the magnitude of the value change must exceed a user-defined dead-band parameter. The output is HIGH during the single schema compute cycle in which the signal value change was detected; otherwise it is LOW.
• Output

indicates if the broadcast transmissions are being received regularly (i.e., indicates if the network link is good). It is LOW while transmissions are regularly received, and the output is HIGH if the operator has not received a broadcast in a user-specified time interval (the Broadcast Dead-Time property of the receiver).
Analog broadcast signals are encoded into 16-bit integer messages that can assume

distinct values. The broadcasted message can represent a floating-point value, an unsigned integer in the range
[0,65535
], or a signed integer in the range
[-32768,32767
].
When configured to decode floating-point values, the receiver operator maps the 16-bit message m into an analog value in the range

as follows:

The signal mappings

and

are properties of the receiver operator. The broadcast operator uses its own signal mapping properties (

and

) to encode the broadcast signal. If the receiver mapping properties are not the same as the broadcast mapping properties, the output of the receiver operator will not be the same as the input to the broadcast operator.

When configured to decode an unsigned integer message, the receiver output is simply the raw transmitted value in the range
[0,65535
]. The same is true for decoding signed integer messages, with the exception that the output range is
[-32768,32767
].

In order to associate a receiver operator to a particular network broadcast, the generic operator must be linked to a specific network channel in the physical hardware, and its signal name property must match the broadcast signal name exactly. Signal names are case sensitive---Design Pad considers the names "OilPressure", "oilPressure", and "OILPRESSURE" to refer to different signals.

User-Defined Properties:
Signal Name. A string label that identifies the broadcast signal that the receiver is "tuned" to. Design Pad associates this receiver operator in one schema with a broadcast operator in another schema that has the same signal name.

Maximum Broadcast Dead-Time. The period of time (in milliseconds) that may elapse before the receiver operator indicates that it has not received a broadcast signal (switches output

to HIGH). Output

remains LOW while the operator actively receives the broadcasted signal.

Network Data Format. Determines the format of the transmitted message: Analog Range, Unsigned Integer, or Signed Integer. The Analog Range setting is used to transmit floating-point values linearly mapped between

and

---see 0% Mapping and 100% Mapping properties below.
0% Mapping. The lower limit of the

output signal range,

100% Mapping. The upper limit of the

output signal range,

.
Display Value Change of Value Output. This property determines if the error output pin

is visible in the schema diagram. Design Pad issues a warning upon processing the schema when the pin is visible but not connected. The warning message is not issued when the pin is not visible (when this property is not checked).
Display Error Output. This property determines if the error output pin

is visible in the schema diagram. Design Pad issues a warning upon processing the schema when the pin is visible but not connected. The warning message is not issued when the pin is not visible (when this property is not checked).
Change of Value Dead-Band. This parameter determines the magnitude of the signal change that must be detected in order for output

to declare that the signal has changed value. For example, if this property is set to 0.1, and the broadcast value changes from 39.50 to 39.58, the operator will declare that the value has not changed. If the value next changes to 39.62, the operator will declare that the value has changed (relative to 39.50). The next value change indication will not occur until the received broadcast signal is 39.52 or 39.72.

Comments: None.

See Also:
Modbus Register Broadcast, Modbus Coil Receiver, Modbus Coil Broadcast