Modbus - DC Brick – Tinkerforge

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# Modbus - DC Brick

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

## API

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

### Basic Functions

`BrickDC.``set_velocity`

  Function ID: | 1

  Request:

  - velocity -- int16

  Response: | no response

  Sets the velocity of the motor. Whereas -32767 is full speed backward, 0 is stop and 32767 is full speed forward. Depending on the acceleration (see `set_acceleration`), the motor is not immediately brought to the velocity but smoothly accelerated.

  The velocity describes the duty cycle of the PWM with which the motor is controlled, e.g. a velocity of 3277 sets a PWM with a 10% duty cycle. You can not only control the duty cycle of the PWM but also the frequency, see `set_pwm_frequency`.

  The default velocity is 0.

`BrickDC.``get_velocity`

  Function ID: | 2
  Request: | empty payload

  Response:

  - velocity -- int16

  Returns the velocity as set by `set_velocity`.

`BrickDC.``get_current_velocity`

  Function ID: | 3
  Request: | empty payload

  Response:

  - velocity -- int16

  Returns the current velocity of the motor. This value is different from `get_velocity` whenever the motor is currently accelerating to a goal set by `set_velocity`.

`BrickDC.``set_acceleration`

  Function ID: | 4

  Request:

  - acceleration -- uint16

  Response: | no response

  Sets the acceleration of the motor. It is given in velocity/s. An acceleration of 10000 means, that every second the velocity is increased by 10000 (or about 30% duty cycle).

  For example: If the current velocity is 0 and you want to accelerate to a velocity of 16000 (about 50% duty cycle) in 10 seconds, you should set an acceleration of 1600.

  If acceleration is set to 0, there is no speed ramping, i.e. a new velocity is immediately given to the motor.

  The default acceleration is 10000.

`BrickDC.``get_acceleration`

  Function ID: | 5
  Request: | empty payload

  Response:

  - acceleration -- uint16

  Returns the acceleration as set by `set_acceleration`.

`BrickDC.``full_brake`

  Function ID: | 8
  Request: | empty payload
  Response: | no response

  Executes an active full brake.

  Warning

  This function is for emergency purposes, where an immediate brake is necessary. Depending on the current velocity and the strength of the motor, a full brake can be quite violent.

  Call `set_velocity` with 0 if you just want to stop the motor.

`BrickDC.``enable`

  Function ID: | 12
  Request: | empty payload
  Response: | no response

  Enables the driver chip. The driver parameters can be configured (velocity, acceleration, etc) before it is enabled.

`BrickDC.``disable`

  Function ID: | 13
  Request: | empty payload
  Response: | no response

  Disables the driver chip. The configurations are kept (velocity, acceleration, etc) but the motor is not driven until it is enabled again.

`BrickDC.``is_enabled`

  Function ID: | 14
  Request: | empty payload

  Response:

  - enabled -- bool

  Returns true if the driver chip is enabled, false otherwise.

### Advanced Functions

`BrickDC.``set_pwm_frequency`

  Function ID: | 6

  Request:

  - frequency -- uint16

  Response: | no response

  Sets the frequency (in Hz) of the PWM with which the motor is driven. The possible range of the frequency is 1-20000Hz. Often a high frequency is less noisy and the motor runs smoother. However, with a low frequency there are less switches and therefore fewer switching losses. Also with most motors lower frequencies enable higher torque.

  If you have no idea what all this means, just ignore this function and use the default frequency, it will very likely work fine.

  The default frequency is 15 kHz.

`BrickDC.``get_pwm_frequency`

  Function ID: | 7
  Request: | empty payload

  Response:

  - frequency -- uint16

  Returns the PWM frequency (in Hz) as set by `set_pwm_frequency`.

`BrickDC.``get_stack_input_voltage`

  Function ID: | 9
  Request: | empty payload

  Response:

  - voltage -- uint16

  Returns the stack input voltage in mV. The stack input voltage is the voltage that is supplied via the stack, i.e. it is given by a Step-Down or Step-Up Power Supply.

`BrickDC.``get_external_input_voltage`

  Function ID: | 10
  Request: | empty payload

  Response:

  - voltage -- uint16

  Returns the external input voltage in mV. The external input voltage is given via the black power input connector on the DC Brick.

  If there is an external input voltage and a stack input voltage, the motor will be driven by the external input voltage. If there is only a stack voltage present, the motor will be driven by this voltage.

  Warning

  This means, if you have a high stack voltage and a low external voltage, the motor will be driven with the low external voltage. If you then remove the external connection, it will immediately be driven by the high stack voltage.

`BrickDC.``get_current_consumption`

  Function ID: | 11
  Request: | empty payload

  Response:

  - voltage -- uint16

  Returns the current consumption of the motor in mA.

`BrickDC.``set_drive_mode`

  Function ID: | 17

  Request:

  - mode -- uint8

  Response: | no response

  Sets the drive mode. Possible modes are:

  - 0 = Drive/Brake
  - 1 = Drive/Coast

  These modes are different kinds of motor controls.

  In Drive/Brake mode, the motor is always either driving or braking. There is no freewheeling. Advantages are: A more linear correlation between PWM and velocity, more exact accelerations and the possibility to drive with slower velocities.

  In Drive/Coast mode, the motor is always either driving or freewheeling. Advantages are: Less current consumption and less demands on the motor and driver chip.

  The default value is 0 = Drive/Brake.

`BrickDC.``get_drive_mode`

  Function ID: | 18
  Request: | empty payload

  Response:

  - mode -- uint8

  Returns the drive mode, as set by `set_drive_mode`.

`BrickDC.``enable_status_led`

  Function ID: | 238
  Request: | empty payload
  Response: | no response

  Enables the status LED.

  The status LED is the blue LED next to the USB connector. If enabled is is on and it flickers if data is transfered. If disabled it is always off.

  The default state is enabled.

  New in version 2.3.1 (Firmware).

`BrickDC.``disable_status_led`

  Function ID: | 239
  Request: | empty payload
  Response: | no response

  Disables the status LED.

  The status LED is the blue LED next to the USB connector. If enabled is is on and it flickers if data is transfered. If disabled it is always off.

  The default state is enabled.

  New in version 2.3.1 (Firmware).

`BrickDC.``is_status_led_enabled`

  Function ID: | 240
  Request: | empty payload

  Response:

  - enabled -- bool

  Returns true if the status LED is enabled, false otherwise.

  New in version 2.3.1 (Firmware).

`BrickDC.``get_protocol1_bricklet_name`

  Function ID: | 241

  Request:

  - port -- char

  Response:

  - protocol_version -- uint8
  - firmware_version -- uint8[3]
  - name -- char[40]

  Returns the firmware and protocol version and the name of the Bricklet for a given port.

  This functions sole purpose is to allow automatic flashing of v1.x.y Bricklet plugins.

`BrickDC.``get_chip_temperature`

  Function ID: | 242
  Request: | empty payload

  Response:

  - temperature -- int16

  Returns the temperature in °C/10 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 an accuracy of +-15%. Practically it is only useful as an indicator for temperature changes.

`BrickDC.``reset`

  Function ID: | 243
  Request: | empty payload
  Response: | no response

  Calling this function will reset the Brick. Calling this function on a Brick inside of a stack will reset the whole stack.

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

`BrickDC.``get_identity`

  Function ID: | 255
  Request: | empty payload

  Response:

  - uid -- char[8]
  - connected_uid -- char[8]
  - position -- char
  - hardware_version -- uint8[3]
  - firmware_version -- uint8[3]
  - device_identifier -- uint16

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

  The position can be '0'-'8' (stack position).

  The device identifier numbers can be found here.

### Callback Configuration Functions

`BrickDC.``set_minimum_voltage`

  Function ID: | 15

  Request:

  - voltage -- uint16

  Response: | no response

  Sets the minimum voltage in mV, below which the `CALLBACK_UNDER_VOLTAGE` callback is triggered. The minimum possible value that works with the DC Brick is 6V. You can use this function to detect the discharge of a battery that is used to drive the motor. If you have a fixed power supply, you likely do not need this functionality.

  The default value is 6V.

`BrickDC.``get_minimum_voltage`

  Function ID: | 16
  Request: | empty payload

  Response:

  - voltage -- uint16

  Returns the minimum voltage as set by `set_minimum_voltage`

`BrickDC.``set_current_velocity_period`

  Function ID: | 19

  Request:

  - period -- uint16

  Response: | no response

  Sets a period in ms with which the `CALLBACK_CURRENT_VELOCITY` callback is triggered. A period of 0 turns the callback off.

  The default value is 0.

`BrickDC.``get_current_velocity_period`

  Function ID: | 20
  Request: | empty payload

  Response:

  - period -- uint16

  Returns the period as set by `set_current_velocity_period`.

### Callbacks

`BrickDC.``CALLBACK_UNDER_VOLTAGE`

  Function ID: | 21

  Response:

  - voltage -- uint16

  This callback is triggered when the input voltage drops below the value set by `set_minimum_voltage`. The response value is the current voltage given in mV.

`BrickDC.``CALLBACK_EMERGENCY_SHUTDOWN`

  Function ID: | 22
  Response: | empty payload

  This callback is triggered if either the current consumption is too high (above 5A) or the temperature of the driver chip is too high (above 175°C). These two possibilities are essentially the same, since the temperature will reach this threshold immediately if the motor consumes too much current. In case of a voltage below 3.3V (external or stack) this callback is triggered as well.

  If this callback is triggered, the driver chip gets disabled at the same time. That means, `enable` has to be called to drive the motor again.

  Note

  This callback only works in Drive/Brake mode (see `set_drive_mode`). In Drive/Coast mode it is unfortunately impossible to reliably read the overcurrent/overtemperature signal from the driver chip.

`BrickDC.``CALLBACK_VELOCITY_REACHED`

  Function ID: | 23

  Response:

  - velocity -- int16

  This callback is triggered whenever a set velocity is reached. For example: If a velocity of 0 is present, acceleration is set to 5000 and velocity to 10000, `CALLBACK_VELOCITY_REACHED` will be triggered after about 2 seconds, when the set velocity is actually reached.

  Note

  Since we can't get any feedback from the DC motor, this only works if the acceleration (see `set_acceleration`) is set smaller or equal to the maximum acceleration of the motor. Otherwise the motor will lag behind the control value and the callback will be triggered too early.

`BrickDC.``CALLBACK_CURRENT_VELOCITY`

  Function ID: | 24

  Response:

  - velocity -- int16

  This callback is triggered with the period that is set by `set_current_velocity_period`. The response value is the current velocity used by the motor.

  `CALLBACK_CURRENT_VELOCITY` is only triggered after the set period if there is a change in the velocity.

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