When using and configuring CAN messages either RX (receives) or TX (transmitted), the following types of message are available.
Used to store certain bits in a system variable (RX) or to send a certain variable throught the CAN bus (TX).
- Bit Lenght: it is possible to compress the variable selected by choosing the option Compress. This allows the system not to fill the storage.
- Compress (Decimals): sets the number of decimals to use and the limits of the variable (Min-Max), any variable out of the limits will be set to these values. For instance, in the image below the AGL can have a value between -10 and 1000.0 with 2 decimals i.e, if the AGL has a value of 500.43453, it will be compress to 500.43.
- Compress (Bits signed): sets the number the bits and these can be signed i.e, negative values are admitted. It’s necessary to configure Input/Output option. User has to configure the option Input/Output.
- Compress (Bits unsigned): sets the number the bits. User has to configure the option Input/Output.
- Input/Output: these values are used to apply a factor and/or offset after the transformation from binary to decimal value.
When reading data from a CAN bus it is common to have information about the message layout. In that case, let’s consider that the first 3 bits correspond to a certain variable. If that variable is always positive, unsigned has to be selected, if it could be positive or negative select signed. The fields Input/Output are used to make the transformation from binary to decimal, corresponding Input to the decimal value and Output to the binary one. Considering the example shown in the previous figure, the binary number is divided by 10 to make the transformation to decimal, so the variable represented here will go from 0 to 0.7 (as 3 unsigned bits can represent numbers from 0 to 7).
Sometimes, control codes are needed for preventing random errors in transmission, where bits frame is operated and the result is sent to the receiver to check it. To do so the CheckSum option is used.
- Back From-Back To: It sets the stage where CRC will be applied
- Endiannes: indicates how the bytes that it contains are read:
- Big endian: set the value from left to right
- Little endian: set the value from right to left
- Mixed endian: Any devices have this format. If you need to configure, please contact us.
- Type: User can choose the type of CRC that will be applied.
This option is used to discard a certain number of bits from the message (the maximum number of bits that can be skipped with a single “Skip” are 32).
This option is used to send a constant value trough the BUS can, so it is used for TX only.
- Nº Bits: number of bits in which the matcher is performed.
- Value: just accept and send this decimal value among all possible values according to number of bits set.
For example, a matcher of 8 bits with a value of 9 will sent : 0000 1001 .