Modbus - Compass Bricklet

This is the description of the Modbus protocol for the Compass Bricklet. General information and technical specifications for the Compass Bricklet are summarized in its hardware description.

API

A general description of the Modbus protocol structure can be found here.

Basic Functions

BrickletCompass.get_heading
Function ID:
  • 1
Request:
  • empty payload
Response:
  • heading – Type: int16, Range: [-215 to 215 - 1]

Returns the heading in 1/10 degree (north = 0 degree, east = 90 degree).

Alternatively you can use get_magnetic_flux_density and calculate the heading with heading = atan2(y, x) * 180 / PI.

If you want to get the value periodically, it is recommended to use the CALLBACK_HEADING callback. You can set the callback configuration with set_heading_callback_configuration.

BrickletCompass.get_magnetic_flux_density
Function ID:
  • 5
Request:
  • empty payload
Response:
  • x – Type: int32, Range: [-231 to 231 - 1]
  • y – Type: int32, Range: [-231 to 231 - 1]
  • z – Type: int32, Range: [-231 to 231 - 1]

Returns the magnetic flux density (magnetic induction) for all three axis in 1/10 mG (milli Gauss).

If you want to get the value periodically, it is recommended to use the CALLBACK_MAGNETIC_FLUX_DENSITY callback. You can set the callback configuration with set_magnetic_flux_density_callback_configuration.

BrickletCompass.set_configuration
Function ID:
  • 9
Request:
  • data_rate – Type: uint8, Range: See meanings
  • background_calibration – Type: bool
Response:
  • no response

Configures the data rate and background calibration.

  • Data Rate: Sets the data rate that is used by the magnetometer. The lower the data rate, the lower is the noise on the data.
  • Background Calibration: Set to true to enable the background calibration and false to turn it off. If the background calibration is enabled the sensing polarity is flipped once per second to automatically calculate and remove offset that is caused by temperature changes. This polarity flipping takes about 20ms. This means that once a second you will not get new data for a period of 20ms. We highly recommend that you keep the background calibration enabled and only disable it if the 20ms off-time is a problem in your application.

Default values: Data rate of 100Hz and background calibration enabled.

The following meanings are defined for the elements of this function:

For data_rate:

  • 0 = 100Hz
  • 1 = 200Hz
  • 2 = 400Hz
  • 3 = 600Hz
BrickletCompass.get_configuration
Function ID:
  • 10
Request:
  • empty payload
Response:
  • data_rate – Type: uint8, Range: See meanings
  • background_calibration – Type: bool

Returns the configuration as set by set_configuration.

The following meanings are defined for the elements of this function:

For data_rate:

  • 0 = 100Hz
  • 1 = 200Hz
  • 2 = 400Hz
  • 3 = 600Hz

Advanced Functions

BrickletCompass.set_calibration
Function ID:
  • 11
Request:
  • offset – Type: int16[3], Range: [-215 to 215 - 1]
  • gain – Type: int16[3], Range: [-215 to 215 - 1]
Response:
  • no response

Sets offset and gain for each of the three axes.

The Bricklet is factory calibrated. If you want to re-calibrate the Bricklet we recommend that you do the calibration through Brick Viewer.

The calibration is saved in non-volatile memory and only has to be done once.

BrickletCompass.get_calibration
Function ID:
  • 12
Request:
  • empty payload
Response:
  • offset – Type: int16[3], Range: [-215 to 215 - 1]
  • gain – Type: int16[3], Range: [-215 to 215 - 1]

Returns the calibration parameters as set by set_calibration.

BrickletCompass.get_spitfp_error_count
Function ID:
  • 234
Request:
  • empty payload
Response:
  • error_count_ack_checksum – Type: uint32, Range: [0 to 232 - 1]
  • error_count_message_checksum – Type: uint32, Range: [0 to 232 - 1]
  • error_count_frame – Type: uint32, Range: [0 to 232 - 1]
  • error_count_overflow – Type: uint32, Range: [0 to 232 - 1]

Returns the error count for the communication between Brick and Bricklet.

The errors are divided into

  • ACK checksum errors,
  • message checksum errors,
  • framing errors and
  • overflow errors.

The errors counts are for errors that occur on the Bricklet side. All Bricks have a similar function that returns the errors on the Brick side.

BrickletCompass.set_bootloader_mode
Function ID:
  • 235
Request:
  • mode – Type: uint8, Range: See meanings
Response:
  • status – Type: uint8, Range: See meanings

Sets the bootloader mode and returns the status after the requested mode change was instigated.

You can change from bootloader mode to firmware mode and vice versa. A change from bootloader mode to firmware mode will only take place if the entry function, device identifier and CRC are present and correct.

This function is used by Brick Viewer during flashing. It should not be necessary to call it in a normal user program.

The following meanings are defined for the elements of this function:

For mode:

  • 0 = Bootloader
  • 1 = Firmware
  • 2 = Bootloader Wait For Reboot
  • 3 = Firmware Wait For Reboot
  • 4 = Firmware Wait For Erase And Reboot

For status:

  • 0 = OK
  • 1 = Invalid Mode
  • 2 = No Change
  • 3 = Entry Function Not Present
  • 4 = Device Identifier Incorrect
  • 5 = CRC Mismatch
BrickletCompass.get_bootloader_mode
Function ID:
  • 236
Request:
  • empty payload
Response:
  • mode – Type: uint8, Range: See meanings

Returns the current bootloader mode, see set_bootloader_mode.

The following meanings are defined for the elements of this function:

For mode:

  • 0 = Bootloader
  • 1 = Firmware
  • 2 = Bootloader Wait For Reboot
  • 3 = Firmware Wait For Reboot
  • 4 = Firmware Wait For Erase And Reboot
BrickletCompass.set_write_firmware_pointer
Function ID:
  • 237
Request:
  • pointer – Type: uint32, Range: [0 to 232 - 1]
Response:
  • no response

Sets the firmware pointer for write_firmware. The pointer has to be increased by chunks of size 64. The data is written to flash every 4 chunks (which equals to one page of size 256).

This function is used by Brick Viewer during flashing. It should not be necessary to call it in a normal user program.

BrickletCompass.write_firmware
Function ID:
  • 238
Request:
  • data – Type: uint8[64], Range: [0 to 255]
Response:
  • status – Type: uint8, Range: [0 to 255]

Writes 64 Bytes of firmware at the position as written by set_write_firmware_pointer before. The firmware is written to flash every 4 chunks.

You can only write firmware in bootloader mode.

This function is used by Brick Viewer during flashing. It should not be necessary to call it in a normal user program.

BrickletCompass.set_status_led_config
Function ID:
  • 239
Request:
  • config – Type: uint8, Range: See meanings
Response:
  • no response

Sets the status LED configuration. By default the LED shows communication traffic between Brick and Bricklet, it flickers once for every 10 received data packets.

You can also turn the LED permanently on/off or show a heartbeat.

If the Bricklet is in bootloader mode, the LED is will show heartbeat by default.

The following meanings are defined for the elements of this function:

For config:

  • 0 = Off
  • 1 = On
  • 2 = Show Heartbeat
  • 3 = Show Status
BrickletCompass.get_status_led_config
Function ID:
  • 240
Request:
  • empty payload
Response:
  • config – Type: uint8, Range: See meanings

Returns the configuration as set by set_status_led_config

The following meanings are defined for the elements of this function:

For config:

  • 0 = Off
  • 1 = On
  • 2 = Show Heartbeat
  • 3 = Show Status
BrickletCompass.get_chip_temperature
Function ID:
  • 242
Request:
  • empty payload
Response:
  • temperature – Type: int16, Range: [-215 to 215 - 1]

Returns the temperature in °C as measured inside the microcontroller. The value returned is not the ambient temperature!

The temperature is only proportional to the real temperature and it has bad accuracy. Practically it is only useful as an indicator for temperature changes.

BrickletCompass.reset
Function ID:
  • 243
Request:
  • empty payload
Response:
  • no response

Calling this function will reset the Bricklet. All configurations will be lost.

After a reset you have to create new device objects, calling functions on the existing ones will result in undefined behavior!

BrickletCompass.write_uid
Function ID:
  • 248
Request:
  • uid – Type: uint32, Range: [0 to 232 - 1]
Response:
  • no response

Writes a new UID into flash. If you want to set a new UID you have to decode the Base58 encoded UID string into an integer first.

We recommend that you use Brick Viewer to change the UID.

BrickletCompass.read_uid
Function ID:
  • 249
Request:
  • empty payload
Response:
  • uid – Type: uint32, Range: [0 to 232 - 1]

Returns the current UID as an integer. Encode as Base58 to get the usual string version.

BrickletCompass.get_identity
Function ID:
  • 255
Request:
  • empty payload
Response:
  • uid – Type: char[8]
  • connected_uid – Type: char[8]
  • position – Type: char
  • hardware_version – Type: uint8[3], Range: [0 to 255]
  • firmware_version – Type: uint8[3], Range: [0 to 255]
  • device_identifier – Type: uint16, Range: [0 to 216 - 1]

Returns the UID, the UID where the Bricklet is connected to, the position, the hardware and firmware version as well as the device identifier.

The position can be 'a', 'b', 'c' or 'd'.

The device identifier numbers can be found here

Callback Configuration Functions

BrickletCompass.set_heading_callback_configuration
Function ID:
  • 2
Request:
  • period – Type: uint32, Unit: 1 ms, Range: [0 to 232 - 1], Default: 0
  • value_has_to_change – Type: bool, Default: false
  • option – Type: char, Range: See meanings, Default: 'x'
  • min – Type: int16, Range: [-215 to 215 - 1]
  • max – Type: int16, Range: [-215 to 215 - 1]
Response:
  • no response

The period is the period with which the CALLBACK_HEADING callback is triggered periodically. A value of 0 turns the callback off.

If the value has to change-parameter is set to true, the callback is only triggered after the value has changed. If the value didn't change within the period, the callback is triggered immediately on change.

If it is set to false, the callback is continuously triggered with the period, independent of the value.

It is furthermore possible to constrain the callback with thresholds.

The option-parameter together with min/max sets a threshold for the CALLBACK_HEADING callback.

The following options are possible:

Option Description
'x' Threshold is turned off
'o' Threshold is triggered when the value is outside the min and max values
'i' Threshold is triggered when the value is inside or equal to the min and max values
'<' Threshold is triggered when the value is smaller than the min value (max is ignored)
'>' Threshold is triggered when the value is greater than the min value (max is ignored)

If the option is set to 'x' (threshold turned off) the callback is triggered with the fixed period.

The default value is (0, false, 'x', 0, 0).

The following meanings are defined for the elements of this function:

For option:

  • 'x' = Off
  • 'o' = Outside
  • 'i' = Inside
  • '<' = Smaller
  • '>' = Greater
BrickletCompass.get_heading_callback_configuration
Function ID:
  • 3
Request:
  • empty payload
Response:
  • period – Type: uint32, Unit: 1 ms, Range: [0 to 232 - 1], Default: 0
  • value_has_to_change – Type: bool, Default: false
  • option – Type: char, Range: See meanings, Default: 'x'
  • min – Type: int16, Range: [-215 to 215 - 1]
  • max – Type: int16, Range: [-215 to 215 - 1]

Returns the callback configuration as set by set_heading_callback_configuration.

The following meanings are defined for the elements of this function:

For option:

  • 'x' = Off
  • 'o' = Outside
  • 'i' = Inside
  • '<' = Smaller
  • '>' = Greater
BrickletCompass.set_magnetic_flux_density_callback_configuration
Function ID:
  • 6
Request:
  • period – Type: uint32, Unit: 1 ms, Range: [0 to 232 - 1], Default: 0
  • value_has_to_change – Type: bool, Default: false
Response:
  • no response

The period is the period with which the CALLBACK_MAGNETIC_FLUX_DENSITY callback is triggered periodically. A value of 0 turns the callback off.

If the value has to change-parameter is set to true, the callback is only triggered after the value has changed. If the value didn't change within the period, the callback is triggered immediately on change.

If it is set to false, the callback is continuously triggered with the period, independent of the value.

BrickletCompass.get_magnetic_flux_density_callback_configuration
Function ID:
  • 7
Request:
  • empty payload
Response:
  • period – Type: uint32, Unit: 1 ms, Range: [0 to 232 - 1], Default: 0
  • value_has_to_change – Type: bool, Default: false

Returns the callback configuration as set by set_magnetic_flux_density_callback_configuration.

Callbacks

BrickletCompass.CALLBACK_HEADING
Function ID:
  • 4
Response:
  • heading – Type: int16, Range: [-215 to 215 - 1]

This callback is triggered periodically according to the configuration set by set_heading_callback_configuration.

The response value is the same as get_heading.

BrickletCompass.CALLBACK_MAGNETIC_FLUX_DENSITY
Function ID:
  • 8
Response:
  • x – Type: int32, Range: [-231 to 231 - 1]
  • y – Type: int32, Range: [-231 to 231 - 1]
  • z – Type: int32, Range: [-231 to 231 - 1]

This callback is triggered periodically according to the configuration set by set_magnetic_flux_density_callback_configuration.

The response values are the same as get_magnetic_flux_density.