Receive, Message Receive

Receive messages

• Library:

• Simulink / Messages & Events

  SimEvents

• 

Description

The Receive block extracts data from received messages and writes them to the output signal port. If there are no new messages when the block executes, the block uses the Value source when queue is empty value. Receive and Message Receive blocks are identical blocks.

• Select Hold last value to hold data read from the last message.

• Select Use initial value to write default data.

Ports

Input

Port_1 — Input message

scalar | vector | matrix

The input port for the message.

Data Types: single | double | int8 | int16 | int32 | int64 | uint8 | uint16 | uint32 | uint64 | Boolean | enumerated | bus | fixed point

Output

Port_S — Show whether a message was received

scalar

Outputs 1 if the block receives a message successfully, and 0 otherwise.

Dependencies

To enable this port, select the check box labeled Show receive status.

Data Types: double

Port_1 — Output signal

scalar | vector | matrix

Output port for the signal.

Data Types: single | double | int8 | int16 | int32 | int64 | uint8 | uint16 | uint32 | uint64 | Boolean | enumerated | bus | fixed point

Parameters

Use internal queue — Select to use an internal queue

on (default for SimEvents^®) | off (default for Simulink^®)

Select this check box if you use an internal queue to receive messages.

Programmatic Use

Block Parameter: UseInternalQueue

Type: character vector

Values: 'on' | 'off'

Default: 'on'

Overwrite the oldest element if queue is full — Specify queue overwriting policy

on (default for Simulink) | off (default for SimEvents)

Select this check box to choose between two queue overwriting policies.

• If you select the check box, an incoming message overwrites the oldest if the queue is full.

• If you clear the check box, the block does not accept new messages if the queue is full.

Dependencies

This parameter is visible when you select the box labeled Use internal queue.

Programmatic Use

Block Parameter: QueueOverwriting

Type: character vector

Values: 'on' | 'off'

Default: 'on' (for Simulink) and 'off' (for SimEvents)

Queue length — Specify the length of the message queue

16 (default) | scalar

Specify message queue capacity. The queue length can be specified as a positive integer between 1 and 2²⁶-1 (both included).

Dependencies

This parameter is visible when you select the box labeled Use internal queue.

Programmatic Use

Block Parameter: QueueLength

Type: character vector

Values: '16' | scalar

Default: '16'

Queue type — Specify message queue sorting policy

FIFO (default) | LIFO | Priority

The block supports three message sorting policies:

• First-in-first-out (FIFO) — The oldest message in the storage departs first.

• Last-in-first-out (LIFO) — The newest message in the storage departs first.

• Priority — Messages or entities are sorted based on their priority.

  The priority queue can be used only when the Overwrite the oldest element if queue is full check box is cleared.

  Note

  Priority queue accepts only non-bus scalar and it does not support fixed point data type.

Dependencies

This parameter is visible when you select the box labeled Use internal queue.

Programmatic Use

Block Parameter: QueueType

Type: character vector

Values: 'FIFO' | 'LIFO' | 'Priority'

Default: 'FIFO'

Priority order — Specify message queue priority

Ascending (default) | Descending

Choose the direction of sorting messages based on priority.

• Ascending — Messages with smaller priority values appear in front of the queue.

• Descending — Messages with greater priority values appear in front of the queue.

Dependencies

This parameter is visible when you select the box labeled Use internal queue andQueue type > Priority.

Programmatic Use

Block Parameter: PriorityOrder

Type: character vector

Values: 'Ascending' | 'Descending'

Default: 'Ascending'

Show receive status — Show whether a message was received

off (default) | on

Select this check box to show whether a message was received. If this check box is selected the block outputs 1 if it receives a message successfully, and 0 otherwise.

Programmatic Use

Block Parameter: ShowQueueStatus

Type: character vector

Values: 'on' | 'off'

Default: 'off'

Initial value — Set initial data value

[](unspecified) (default) | scalar | vector | matrix

Enter an initial data value for the queue before the arrival of the first message. The default value [](unspecified) is treated as 0 with data type double.

To use this block to initialize a nonvirtual bus signal, specify the initial value as a MATLAB^® structure. For more information about initializing nonvirtual bus signals using structures, see Specify Initial Conditions for Bus Elements.

Programmatic Use

Block Parameter: InitialValue

Type: character vector

Values: '[]' | scalar

Default: '[]'

Value source when queue is empty — Value source for empty queue

Hold last value (default) | Use initial value

Specify the value to receive when received message queue is empty.

• Hold last value (default) — Holds data read from the last message.

  Initially, if the block tries to receive a message and fails, it outputs the initial value.

• Use initial value — Writes default data.

Dependencies

This parameter is visible when you select the box labeled Use internal queue.

Programmatic Use

Block Parameter: ValueSourceWhenQueueIsEmpty

Type: character vector

Values: 'Hold last value' | 'Use initial value'

Default: 'Hold last value'

Sample time (-1 for inherited) — Specify the time interval between samples

-1 (default) | scalar

To inherit the sample time, set this parameter to -1. See Specify Sample Time for more information.

Programmatic Use

Block Parameter: SampleTime

Type: character vector

Values: '-1' | scalar

Default: '-1'

Model Examples

Animate and Understand Sending and Receiving Messages

Send, receive, visualize, and animate messages and display message data.

Use a Queue Block to Manage Messages

Use FIFO queue, LIFO queue, and priority queue to sort and store messages and define queue policies.

Establish Message Send and Receive Interfaces Between Software Components

Create message send and receive interfaces, and prepare components for C++ code generation.

Model a Message Receive Interface that Runs on Message Availability

Synchronize execution with data availability in message-based systems. We show how to model this behavior using events and actions. This example builds on another example, Establish Message Send and Receive Interfaces Between Software Components, where two software components communicate using messages.

Block Characteristics

Data Types	Boolean | bus | double | enumerated | fixed point | integer | single | string
Direct Feedthrough	no
Multidimensional Signals	yes
Variable-Size Signals	no
Zero-Crossing Detection	no

Extended Capabilities

C/C++ Code Generation
Generate C and C++ code using Simulink® Coder™.