Packing and Unpacking Messages
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The CAN Pack/Unpack blocks provide a mechanism to specify the structure of a message using the signals table containining the field name, start bit, length etc for each value sent.
Are there similar blocks that provide the same mechanism for specifiying the message format but that aren't specifically for sending CAN messages?
I have a model to update which currently does all of the bit packing/shifting/concatenation in a very manual and time consuming way.
2 comentarios
Dimitri MANKOV
el 20 de Jul. de 2022
Hi Scott,
Which message type are you trying to generate / what protocol do you intend to use? There are similar helper blocks for different purposes, but each of them is quite specific in its design...
Best,
Dimitri
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Dimitri MANKOV
el 20 de Jul. de 2022
Hi Scott,
There are different formats used by serial devices to send and receive data. The Simulink model thus must be able to produce (send) and understand (receive) data in the required format. Simulink is designed to handle numerical data, while the actual serial data may be strings or bytes of data in a particular format. This means that some encoding/decoding using blocks included with Simulink Real-Time is necessary. Configuration of the lower-level serial protocol may also be needed, depending on the external device requirements.
Typically, serial devices communicate using either:
- Binary format: data is packed into bytes, in a format specified by the device. You cannot interpret the data just by looking at the stream of bytes and must have knowledge about the format to encode/decode it properly.
- ASCII format: device sends strings back and forth, which are usually user-readable.
There are several Simulink Real-Time examples showing how this encoding can be done here. In addition, Speedgoat recently released a series of product examples with their latest I/O Blockset version (v9.4.1), including an example showing a typical RS485 configuration. You can check them out here.
I hope this is helpful!
Dimitri
3 comentarios
Dimitri MANKOV
el 20 de Jul. de 2022
Hi Scott,
I'm not aware of any similar block specifically designed for RS232/RS485-based protocols, but I guess it would be possible to misuse the CAN Pack block as follows:
![](https://www.mathworks.com/matlabcentral/answers/uploaded_files/1071865/image.png)
Would that approach fulfill your requirements? Note that using a Mux block to create a vector of uint8 values before passing it to the driver blocks would work just as well.
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