CAN Bus protocol
This section defines the MEX communication protocol.
On the one hand, there are some specific messages that are already configured internally in the system so no configuration in MEX is required for them. Consequently, the device that is intended to communicate with MEX must correctly configure those messages. This message configuration is detailed below in the Application processor section.
On the other hand, it is also detailed the structure of other messages that are not contemplated by default in the MEX configuration but that can be carried out for communication and operation with other devices.
Application processor
This is the configuration of specific messages that must perform any device to communicate with MEX.
Note
No configuration of these messages is required in MEX, as it is already internally configured to process messages configured in this way.
For these messages to be processed correctly, they must be received by the 'Consumer' Application processor.
MEX Communication Protocol over CAN bus is defined as follows:
-
cmd (8 bits - 1 byte): first byte refers to the Message Type.
Messages Type are defined as follows:
| Type | Value | Description |
|---|---|---|
| t_arbitration | 0 | Arbitration message |
| t_version | 1 | Version request / response |
| t_pwm_0_3_set | 2 | PWMs 0 to 3 |
| t_pwm_4_7_set | 3 | PWMs 4 to 7 |
| 4 | Reserved | |
| t_esc_tm | 5 | Scorpion Tribunus ESC telemetry data |
| t_esc_tm2 | 6 | Jeti ESC telemetry data |
| t_bec_tm1 | 7 | Jeti BEC telemetry data 1 |
| t_bec_tm2 | 8 | Jeti BEC telemetry data 2 |
| t_temp_tm | 9 | Jeti Temperature sensor telemetry data |
| t_mcu_cmd | 10 | MCU battery command |
| t_pwm_8_11_set | 11 | PWMs 8 to 11 |
| t_pwm_12_15_set | 12 | PWMs 12 to 15 |
| t_pwm_16_19_set | 13 | PWMs 16 to 19 |
| 14 | Reserved | |
| 15 | Reserved | |
| t_cmd_maint | 16 | Command to go to Maintenance Mode |
| t_stick_sel | 17 | Command for Stick selection |
| t_mcu_tm1 | 18 | MCU telemetry data 1 |
| t_mcu_tm2 | 19 | MCU telemetry data 2 |
Note
All these Message Type are defined as a "Matcher" in the CAN custom messages configuration. For example, for PWMs 0-3, the Message Type will be configured as follows:
- Value: 2, since it is the value for the message for PWMs 0 to 3 (it is indifferent to the PWM number).
- Bits: 8, because the Message Type is an 8-bit message.
- data (up to 56 bits - 8 bytes): The following bytes refer to the Message data .
Next sections decribe each one of the possible messages with an example. The following examples include complete messages, so each beginning corresponds to Message Type.
MEX Status
MEX status message is composed as follows:
| Type | Value | Bits | Description |
|---|---|---|---|
| cmd (t_version) | 1 | 8 | Version request / response |
| data | - | 8 | Version - Major |
| data | - | 8 | Version - Minor |
| data | - | 8 | Version - Revision |
| data (sysaddr) | - | 8 | Serial number - address 0 |
| data (sysaddr) | - | 8 | Serial number - address 1 |
| data | - | 1 | System Error bit (ID 7) |
| data (MEX status) | - | 1 | System power up bit error bit (ID 12) |
| data (MEX status) | - | 1 | PDI error bit (ID 9) |
| data (MEX status) | - | 1 | Memory Allocationbit (ID 8) |
| data (MEX status) | - | 1 | File system error bit (ID 6) |
| data (MEX status) | - | 1 | CAN A ERROR bit (ID 73) |
| data (MEX status) | - | 1 | CAN B ERROR bit (ID 74) |
| data (MEX status) | - | 1 | false |
| data (MEX status) | - | 1 | Arbiter enabled |
| data (MEX status) | - | 1 | Arbiter status |
Arbitration
MEX Arbitration Status message is composed as follows:
- Message 1: Sent when "Send status" is enabled
| Type | Value | Bits | Description |
|---|---|---|---|
| cmd (t_arbitration) | 0 | 8 | Arbitration message |
| Flag | 255 ([0xFF]) | 8 | Status Flag |
| CAP | - | 7 | Active Autopilot (Current) |
| data | - | 1 | Arbitrating |
| data | - | 1 | AP0 Alive |
| data | - | 1 | AP1 Alive |
| data | - | 1 | AP2 Alive |
| data | - | 1 | AP3 Alive (External) |
| data | - | 1 | AP0 Ready |
| data | - | 1 | AP1 Ready |
| data | - | 1 | AP2 Ready |
| data | - | 1 | AP3 Ready (External) |
| data (MEX status) | - | 1 | System bit error (ID 7) |
| data (MEX status) | - | 1 | System power up bit error (ID 12) |
| data (MEX status) | - | 1 | PDI bit error (ID 9) |
| data (MEX status) | - | 1 | Memory Allocation bit (ID 8) |
| data (MEX status) | - | 1 | File system bit error (ID 6) |
| data (MEX status) | - | 1 | CAN A bit error (ID 73) |
| data (MEX status) | - | 1 | CAN B bit error (ID 74) |
| data (MEX status) | - | 1 | false |
| data (MEX status) | - | 1 | Arbiter enabled |
| data (MEX status) | - | 1 | Arbiter status |
- Message 2 (One for each Veronte Autopilot 1x): Sent when "Send score" is enabled
| Type | Value | Bits | Description |
|---|---|---|---|
| cmd (t_arbitration) | 0 | 8 | Arbitration message |
| data | - | 8 | Autopilot ID [0, 3] |
| data | - | 32 (4 bytes) | Autopilot score as Float |
Command PWMs
Each PWM in MEX has to be associated to a Sub Id that indicates which CAN Bus message's PWM is listening to.
That allows to control up to four PWMs using the same message if it is desired. Each message is composed by 4 PWMs maximum.
- PWMs from 0 to 3 are sent in a message that includes 4 PWMs coded as 12-bit integers:
| Type | Value | Bits | Description |
|---|---|---|---|
| cmd (t_pwm_0_3_set) | 2 | 8 | PWMs 0 to 3 |
| data (pwm0) | - | 12 | PWM value for sub-id 0 |
| data (pwm1) | - | 12 | PWM value for sub-id 1 |
| data (pwm2) | - | 12 | PWM value for sub-id 2 |
| data (pwm3) | - | 12 | PWM value for sub-id 3 |
- PWMs from 4 to 7 are sent in a message that includes 4 PWMs coded as 12-bit integers:
| Type | Value | Bits | Description |
|---|---|---|---|
| cmd (t_pwm_4_7_set) | 3 | 8 | PWMs 4 to 7 |
| data (pwm0) | - | 12 | PWM value for sub-id 4 |
| data (pwm1) | - | 12 | PWM value for sub-id 5 |
| data (pwm2) | - | 12 | PWM value for sub-id 6 |
| data (pwm3) | - | 12 | PWM value for sub-id 7 |
- PWMs from 8 to 11 are sent in a message that includes 4 PWMs coded as 12-bit integers:
| Type | Value | Bits | Description |
|---|---|---|---|
| cmd (t_pwm_8_11_set) | 11 | 8 | PWMs 8 to 11 |
| data (pwm0) | - | 12 | PWM value for sub-id 8 |
| data (pwm1) | - | 12 | PWM value for sub-id 9 |
| data (pwm2) | - | 12 | PWM value for sub-id 10 |
| data (pwm3) | - | 12 | PWM value for sub-id 11 |
- PWMs from 12 to 15 are sent in a message that includes 4 PWMs coded as 12-bit integers:
| Type | Value | Bits | Description |
|---|---|---|---|
| cmd (t_pwm_12_15_set) | 12 | 8 | PWMs 12 to 15 |
| data (pwm0) | - | 12 | PWM value for sub-id 12 |
| data (pwm1) | - | 12 | PWM value for sub-id 13 |
| data (pwm2) | - | 12 | PWM value for sub-id 14 |
| data (pwm3) | - | 12 | PWM value for sub-id 15 |
- PWMs from 16 to 19 are sent in a message that includes 4 PWMs coded as 12-bit integers:
| Type | Value | Bits | Description |
|---|---|---|---|
| cmd (t_pwm_16_19_set) | 13 | 8 | PWMs 16 to 19 |
| data (pwm0) | - | 12 | PWM value for sub-id 16 |
| data (pwm1) | - | 12 | PWM value for sub-id 17 |
| data (pwm2) | - | 12 | PWM value for sub-id 18 |
| data (pwm3) | - | 12 | PWM value for sub-id 19 |
A complete example of how to command PWMs from Veronte Autopilot 1x and read them into MEX can be consulted in the Commanding/Reading PWMs - Integration examples section of the MEX PDI Builder user manual.
MCU telemetry
From MEX
The telemetry sent by MEX through CAN Bus is composed by:
- Message 1:
| Type | Value | Bits | Description |
|---|---|---|---|
| cmd (t_mcu_tm1) | 18 | 8 | MCU telemetry data 1 |
| data | - | 8 | Battery Serial Number [0] |
| data | - | 8 | Battery Serial Number [1] |
| data | - | 8 | Battery Temperature (as received from MCU) |
| data | - | 8 | Low Cell Voltage (as received from MCU) |
| - | 4 | Reserved (Zeros) | |
| data (Status Bit) | - | 1 | PWM receiving Ok |
| data (Status Bit) | - | 1 | CAN PWM receiving Ok |
| data (Status Bit) | - | 1 | CAN B receiving |
| data (Status Bit) | - | 1 | CAN A receiving |
- Message 2:
| Type | Value | Bytes | Description |
|---|---|---|---|
| cmd (t_mcu_tm2) | 19 | 1 | MCU telemetry data 2 |
| data | - | 1 | Battery Serial Number [2] |
| data | - | 1 | Battery Serial Number [3] |
| data | - | 1 | Battery Serial Number [4] |
| data | - | 1 | Battery Serial Number [5] |
| data | - | 1 | Battery Serial Number [6] |
| data | - | 1 | Battery Serial Number [7] |
To MEX
The telemetry sent to MEX must be configured as follows:
| Type | Value | Bytes | Description |
|---|---|---|---|
| cmd (t_mcu_cmd) | 10 | 1 | MCU battery command |
| data | - | 1 | SUB-id A |
| data | - | 1 | LED Value A |
| data | - | 1 | SUB-id B |
| data | - | 1 | LED Value B |
| data | - | 1 | SUB-id C |
| data | - | 1 | LED Value C |
Each MEX will use the SUB-id of the PWM associated to the "Scorpion Tribunus"/PWM ID to identify the value to be used.
Scorpion Tribunus ESC Telemetry
The telemetry read from the Scorpion ESC is sent as:
| Type | Value | Bytes | Description |
|---|---|---|---|
| cmd (t_esc_tm) | 5 | 1 | Scorpion Tribunus ESC telemetry data |
| data | - | 1 | Input voltage in range [0, 85] |
| data | - | 1 | Temperature in Celsius |
| data | - | 1 | Error Flags from the ESC |
| data | - | 1 | Current in Amps [0, 255] |
| data | - | 1 | Consumption in mAmps [0, 25500] |
| data | - | 1 | RPMs [0, 25500] |
| data | - | 1 | Throttle as percentage*2 [0, 200] |
JetiTM ESC Telemetry
The telemetry read from Jeti-TM compatible ESCs is sent as:
| Type | Value | Bytes | Description |
|---|---|---|---|
| cmd (t_esc_tm2) | 6 | 1 | Jeti ESC telemetry data |
| data | - | 1 | Throttle value [0, 200] |
| data | - | 2 | Current RPMs |
| data | - | 10 bits | Input voltage in the range [0, 70] Volts |
| data | - | 10 bits | Temperature in the range [0, 575] Kelvin |
| data | - | 12 bits | Current in the range [0, 400.0] Amps |
Jeti BEC Telemetry
The telemetry read from Jeti BEC will be sent in 2 different messages:
- Message 1:
| Type | Value | Bits | Description |
|---|---|---|---|
| cmd (t_bec_tm1) | 7 | 8 | Jeti BEC telemetry data 1 |
| data | - | 16 | Device ID |
| data | - | 12 | Input voltage in the range [0, 70] Volts |
| data | - | 12 | Output voltage in the range [0, 70] Volts |
| data | - | 12 | Temperature in the range [0, 575] Kelvin |
- Message 2:
| Type | Value | Bits | Description |
|---|---|---|---|
| cmd (t_bec_tm2) | 8 | 8 | Jeti BEC telemetry data 2 |
| data | - | 16 | Device ID |
| data | - | 12 | Current in range [0, 100.0] Amps |
Jeti Temperature Sensor Telemetry
The telemetry read from a Jeti Temperature sensor will be sent as:
| Type | Value | Bits | Description |
|---|---|---|---|
| cmd (t_temp_tm) | 9 | 8 | Jeti Temperature sensor telemetry data |
| data | - | 16 | Device ID |
| data | - | 12 | Measured temperature 1 in the range [0, 750] Kelvin |
| data | - | 12 | Measured temperature 2 in the range [0, 750] Kelvin |
Set Maintenance Mode Command
This command will configure the MEX in maintenance mode, setting its configuration in a way that communications can work over SCI-A, SCI-B or Serial-to-CAN configured as:
- SCI-A and SCI-B: 115200 bauds, 8 data bits, 1 stop, no parity.
- Serial to CAN:
- TX Id: 1301
- RX Id: 1301
The format of the command is:
| Type | Value | Bytes | Description |
|---|---|---|---|
| cmd (t_cmd_maint) | 16 | 1 | Command to go to Maintenance Mode |
Stick Selection Command
This command is used to enable or disable the MEX PPM reader. If address received matches the MEX's one, MEX PPM reader will be enabled, otherwise it will be disabled.
The format of the command is:
| Type | Value | Bytes | Description |
|---|---|---|---|
| cmd (t_stick_sel) | 17 | 1 | Command for Stick selection |
| data (sysaddr) | - | 1 | address 0 |
| data (sysaddr) | - | 1 | address 1 |
MEX as external magnetometer
In this section it is explained how to configure the MEX magnetometer to be used as an external magnetometer for another device, either via CAN or serial.
CAN
The CAN messages sent by MEX must have the following structure:
- CAN Id: It can be in standard frame format (11-bits) or in extended frame format (29-bits). The CAN Id frame format will depend on the CAN protocol supported by the receiving device.
- Variables: The MEX variables associated with the magnetic data are:
- ID 313: Magnetometer - X Body Axis
- ID 314: Magnetometer - Y Body Axis
- ID 315: Magnetometer - Z Body Axis
In addition, users must configure the sending period and endianness of these messages, as well as the baudrate of the CAN bus.
Note
Detailed information on how to build CAN messages can be consulted in the Custom Messages types - Input/Output section of the 1x PDI Builder user manual.
The device receiving this information, must be configured properly so that it matches what has been configured in MEX.
Serial
The serial messages sent by MEX must have the following structure:
- Variables: The MEX variables associated with the magnetic data are:
- ID 313: Magnetometer - X Body Axis
- ID 314: Magnetometer - Y Body Axis
- ID 315: Magnetometer - Z Body Axis
- Checksum: It is useful to include a checksum to verify that the message is sent and received correctly.
In addition, users must configure the sending period of these messages, as well as the baudrate of the serial port (RS232/RS485).
Note
Detailed information on how to build CAN messages can be consulted in the Custom Messages types - Input/Output section of the 1x PDI Builder user manual.
The device receiving this information, must be configured properly so that it matches what has been configured in MEX.
Communication with MEX
MEX can also be used to receive data through a communication protocol and transmit it through another.
Serial reception and CAN transmission
- For serial reception, follow the steps below:
-
Set the baudrate of the serial port used, RS232 or RS485.
-
In order to communicate with the device sending the data, serial messages must be built to match the serial protocol specified by that device.
Note
Normally, it contains the variables to be stored in MEX and a checksum to verify that the message is sent and received correctly. Please refer to the list of variables in this manual to see the variables available in MEX.
-
Configure the timeout of the messages. Remember that it has to be higher than the message sending period specified in the sending device.
-
Set the time to idle for these messages.
- For CAN transmission, follow the steps below:
-
Build a CAN message with the following structure:
-
CAN Id: It can be in standard frame format (11-bits) or in extended frame format (29-bits). The CAN Id frame format will depend on the CAN protocol supported by the receiving device.
-
Variables: The variables in which the information received via serial has been stored must be set.
Please refer to the list of variables in this manual to see the variables available in MEX.
-
-
Configure the sending period and endianness of these messages, as well as the baudrate of the CAN bus.
The device receiving this information, must be configured properly so that it matches what has been configured in MEX.
CAN reception and serial transmission
- For CAN reception, follow the steps below:
-
In order to communicate with the device sending the data, the CAN messages must be built to match the CAN protocol specified by that device.
Note
Normally, it is composed of a CAN Id and variables to be stored in MEX. Please refer to the list of variables in this manual to see the variables available in MEX.
-
Configure the sending period and endianness of these messages, as well as the baudrate of the CAN bus.
- For serial transmission, follow the steps below:
-
Build a serial message with the variables received via CAN:
-
Variables: The variables in which the information received via CAN has been stored must be set.
Please refer to the list of variables in this manual to see the variables available in MEX.
-
Checksum: It is useful to include a checksum to verify that the message is sent and received correctly.
-
-
Configure the sending period of these messages, as well as the baudrate of the serial port (RS232/RS485).
The device receiving this information, must be configured properly so that it matches what has been configured in MEX.
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