Specifications / Modbus Protocol / API / Bricks (Discontinued) / Stepper Brick

Modbus - Stepper Brick¶

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

API¶

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

Basic Functions¶

BrickStepper.set_max_velocity¶

Function ID:	1
Request:	velocity – Type: uint16, Unit: 1 1/s, Range: [0 to 2¹⁶ - 1]
Response:	no response

Sets the maximum velocity of the stepper motor. This function does not start the motor, it merely sets the maximum velocity the stepper motor is accelerated to. To get the motor running use either set_target_position, set_steps, drive_forward or drive_backward.

BrickStepper.get_max_velocity¶

Function ID:	2
Request:	empty payload
Response:	velocity – Type: uint16, Unit: 1 1/s, Range: [0 to 2¹⁶ - 1]

Returns the velocity as set by set_max_velocity.

BrickStepper.get_current_velocity¶

Function ID:	3
Request:	empty payload
Response:	velocity – Type: uint16, Unit: 1 1/s, Range: [0 to 2¹⁶ - 1]

Returns the current velocity of the stepper motor.

BrickStepper.set_speed_ramping¶

Function ID:	4
Request:	acceleration – Type: uint16, Unit: 1 1/s², Range: [0 to 2¹⁶ - 1], Default: 1000 deacceleration – Type: uint16, Unit: 1 1/s², Range: [0 to 2¹⁶ - 1], Default: 1000
Response:	no response

Sets the acceleration and deacceleration of the stepper motor. An acceleration of 1000 means, that every second the velocity is increased by 1000 steps/s.

For example: If the current velocity is 0 and you want to accelerate to a velocity of 8000 steps/s in 10 seconds, you should set an acceleration of 800 steps/s².

An acceleration/deacceleration of 0 means instantaneous acceleration/deacceleration (not recommended)

BrickStepper.get_speed_ramping¶

Function ID:	5
Request:	empty payload
Response:	acceleration – Type: uint16, Unit: 1 1/s², Range: [0 to 2¹⁶ - 1], Default: 1000 deacceleration – Type: uint16, Unit: 1 1/s², Range: [0 to 2¹⁶ - 1], Default: 1000

Returns the acceleration and deacceleration as set by set_speed_ramping.

BrickStepper.full_brake¶

Function ID:	6
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 stop if you just want to stop the motor.

BrickStepper.set_steps¶

Function ID:	11
Request:	steps – Type: int32, Range: [-2³¹ to 2³¹ - 1]
Response:	no response

Sets the number of steps the stepper motor should run. Positive values will drive the motor forward and negative values backward. The velocity, acceleration and deacceleration as set by set_max_velocity and set_speed_ramping will be used.

BrickStepper.get_steps¶

Function ID:	12
Request:	empty payload
Response:	steps – Type: int32, Range: [-2³¹ to 2³¹ - 1]

Returns the last steps as set by set_steps.

BrickStepper.get_remaining_steps¶

Function ID:	13
Request:	empty payload
Response:	steps – Type: int32, Range: [-2³¹ to 2³¹ - 1]

Returns the remaining steps of the last call of set_steps. For example, if set_steps is called with 2000 and get_remaining_steps is called after the motor has run for 500 steps, it will return 1500.

BrickStepper.drive_forward¶

Function ID:	16
Request:	empty payload
Response:	no response

Drives the stepper motor forward until drive_backward or stop is called. The velocity, acceleration and deacceleration as set by set_max_velocity and set_speed_ramping will be used.

BrickStepper.drive_backward¶

Function ID:	17
Request:	empty payload
Response:	no response

Drives the stepper motor backward until drive_forward or stop is triggered. The velocity, acceleration and deacceleration as set by set_max_velocity and set_speed_ramping will be used.

BrickStepper.stop¶

Function ID:	18
Request:	empty payload
Response:	no response

Stops the stepper motor with the deacceleration as set by set_speed_ramping.

BrickStepper.set_motor_current¶

Function ID:	22
Request:	current – Type: uint16, Unit: 1 mA, Range: [100 to 2291], Default: 800
Response:	no response

Sets the current with which the motor will be driven.

Warning

Do not set this value above the specifications of your stepper motor. Otherwise it may damage your motor.

BrickStepper.get_motor_current¶

Function ID:	23
Request:	empty payload
Response:	current – Type: uint16, Unit: 1 mA, Range: [100 to 2291], Default: 800

Returns the current as set by set_motor_current.

BrickStepper.enable¶

Function ID:	24
Request:	empty payload
Response:	no response

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

BrickStepper.disable¶

Function ID:	25
Request:	empty payload
Response:	no response

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

Warning

Disabling the driver chip while the motor is still turning can damage the driver chip. The motor should be stopped calling stop function before disabling the motor power. The stop function will not wait until the motor is actually stopped. You have to explicitly wait for the appropriate time after calling the stop function before calling the disable function.

BrickStepper.is_enabled¶

Function ID:	26
Request:	empty payload
Response:	enabled – Type: bool, Default: false

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

Advanced Functions¶

BrickStepper.set_current_position¶

Function ID:	7
Request:	position – Type: int32, Range: [-2³¹ to 2³¹ - 1]
Response:	no response

Sets the current steps of the internal step counter. This can be used to set the current position to 0 when some kind of starting position is reached (e.g. when a CNC machine reaches a corner).

BrickStepper.get_current_position¶

Function ID:	8
Request:	empty payload
Response:	position – Type: int32, Range: [-2³¹ to 2³¹ - 1]

Returns the current position of the stepper motor in steps. On startup the position is 0. The steps are counted with all possible driving functions (set_target_position, set_steps, drive_forward or drive_backward). It also is possible to reset the steps to 0 or set them to any other desired value with set_current_position.

BrickStepper.set_target_position¶

Function ID:	9
Request:	position – Type: int32, Range: [-2³¹ to 2³¹ - 1]
Response:	no response

Sets the target position of the stepper motor in steps. For example, if the current position of the motor is 500 and set_target_position is called with 1000, the stepper motor will drive 500 steps forward. It will use the velocity, acceleration and deacceleration as set by set_max_velocity and set_speed_ramping.

A call of set_target_position with the parameter x is equivalent to a call of set_steps with the parameter (x - get_current_position).

BrickStepper.get_target_position¶

Function ID:	10
Request:	empty payload
Response:	position – Type: int32, Range: [-2³¹ to 2³¹ - 1]

Returns the last target position as set by set_target_position.

BrickStepper.set_step_mode¶

Function ID:	14
Request:	mode – Type: uint8, Range: See meanings, Default: 8
Response:	no response

Sets the step mode of the stepper motor. Possible values are:

Full Step = 1
Half Step = 2
Quarter Step = 4
Eighth Step = 8

A higher value will increase the resolution and decrease the torque of the stepper motor.

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

For mode:

1 = Full Step
2 = Half Step
4 = Quarter Step
8 = Eighth Step

BrickStepper.get_step_mode¶

Function ID:	15
Request:	empty payload
Response:	mode – Type: uint8, Range: See meanings, Default: 8

Returns the step mode as set by set_step_mode.

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

For mode:

1 = Full Step
2 = Half Step
4 = Quarter Step
8 = Eighth Step

BrickStepper.get_stack_input_voltage¶

Function ID:	19
Request:	empty payload
Response:	voltage – Type: uint16, Unit: 1 mV, Range: [0 to 2¹⁶ - 1]

Returns the stack input voltage. 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.

BrickStepper.get_external_input_voltage¶

Function ID:	20
Request:	empty payload
Response:	voltage – Type: uint16, Unit: 1 mV, Range: [0 to 2¹⁶ - 1]

Returns the external input voltage. The external input voltage is given via the black power input connector on the Stepper 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

BrickStepper.get_current_consumption¶

Function ID:	21
Request:	empty payload
Response:	current – Type: uint16, Unit: 1 mA, Range: [0 to 2¹⁶ - 1]

Returns the current consumption of the motor.

BrickStepper.set_decay¶

Function ID:	27
Request:	decay – Type: uint16, Range: [0 to 2¹⁶ - 1], Default: 10000
Response:	no response

Sets the decay mode of the stepper motor. A value of 0 sets the fast decay mode, a value of 65535 sets the slow decay mode and a value in between sets the mixed decay mode.

Changing the decay mode is only possible if synchronous rectification is enabled (see set_sync_rect).

For a good explanation of the different decay modes see this blog post by Avayan.

A good decay mode is unfortunately different for every motor. The best way to work out a good decay mode for your stepper motor, if you can't measure the current with an oscilloscope, is to listen to the sound of the motor. If the value is too low, you often hear a high pitched sound and if it is too high you can often hear a humming sound.

Generally, fast decay mode (small value) will be noisier but also allow higher motor speeds.

Note

There is unfortunately no formula to calculate a perfect decay mode for a given stepper motor. If you have problems with loud noises or the maximum motor speed is too slow, you should try to tinker with the decay value

BrickStepper.get_decay¶

Function ID:	28
Request:	empty payload
Response:	decay – Type: uint16, Range: [0 to 2¹⁶ - 1], Default: 10000

Returns the decay mode as set by set_decay.

BrickStepper.set_sync_rect¶

Function ID:	33
Request:	sync_rect – Type: bool, Default: false
Response:	no response

Turns synchronous rectification on or off (true or false).

With synchronous rectification on, the decay can be changed (see set_decay). Without synchronous rectification fast decay is used.

For an explanation of synchronous rectification see here.

Warning

If you want to use high speeds (> 10000 steps/s) for a large stepper motor with a large inductivity we strongly suggest that you disable synchronous rectification. Otherwise the Brick may not be able to cope with the load and overheat.

BrickStepper.is_sync_rect¶

Function ID:	34
Request:	empty payload
Response:	sync_rect – Type: bool, Default: false

Returns true if synchronous rectification is enabled, false otherwise.

BrickStepper.set_time_base¶

Function ID:	35
Request:	time_base – Type: uint32, Unit: 1 s, Range: [0 to 2³² - 1], Default: 1
Response:	no response

Sets the time base of the velocity and the acceleration of the stepper brick.

For example, if you want to make one step every 1.5 seconds, you can set the time base to 15 and the velocity to 10. Now the velocity is 10steps/15s = 1steps/1.5s.

BrickStepper.get_time_base¶

Function ID:	36
Request:	empty payload
Response:	time_base – Type: uint32, Unit: 1 s, Range: [0 to 2³² - 1], Default: 1

Returns the time base as set by set_time_base.

BrickStepper.get_all_data¶

Function ID:	37
Request:	empty payload
Response:	current_velocity – Type: uint16, Unit: 1 1/s, Range: [0 to 2¹⁶ - 1] current_position – Type: int32, Range: [-2³¹ to 2³¹ - 1] remaining_steps – Type: int32, Range: [-2³¹ to 2³¹ - 1] stack_voltage – Type: uint16, Unit: 1 mV, Range: [0 to 2¹⁶ - 1] external_voltage – Type: uint16, Unit: 1 mV, Range: [0 to 2¹⁶ - 1] current_consumption – Type: uint16, Unit: 1 mA, Range: [0 to 2¹⁶ - 1]

Returns the following parameters: The current velocity, the current position, the remaining steps, the stack voltage, the external voltage and the current consumption of the stepper motor.

There is also a callback for this function, see CALLBACK_ALL_DATA callback.

BrickStepper.set_spitfp_baudrate_config¶

Function ID:	231
Request:	enable_dynamic_baudrate – Type: bool, Default: true minimum_dynamic_baudrate – Type: uint32, Unit: 1 Bd, Range: [400000 to 2000000], Default: 400000
Response:	no response

The SPITF protocol can be used with a dynamic baudrate. If the dynamic baudrate is enabled, the Brick will try to adapt the baudrate for the communication between Bricks and Bricklets according to the amount of data that is transferred.

The baudrate will be increased exponentially if lots of data is sent/received and decreased linearly if little data is sent/received.

This lowers the baudrate in applications where little data is transferred (e.g. a weather station) and increases the robustness. If there is lots of data to transfer (e.g. Thermal Imaging Bricklet) it automatically increases the baudrate as needed.

In cases where some data has to transferred as fast as possible every few seconds (e.g. RS485 Bricklet with a high baudrate but small payload) you may want to turn the dynamic baudrate off to get the highest possible performance.

The maximum value of the baudrate can be set per port with the function set_spitfp_baudrate. If the dynamic baudrate is disabled, the baudrate as set by set_spitfp_baudrate will be used statically.

New in version 2.3.6 (Firmware).

BrickStepper.get_spitfp_baudrate_config¶

Function ID:	232
Request:	empty payload
Response:	enable_dynamic_baudrate – Type: bool, Default: true minimum_dynamic_baudrate – Type: uint32, Unit: 1 Bd, Range: [400000 to 2000000], Default: 400000

Returns the baudrate config, see set_spitfp_baudrate_config.

New in version 2.3.6 (Firmware).

BrickStepper.get_send_timeout_count¶

Function ID:	233
Request:	communication_method – Type: uint8, Range: See meanings
Response:	timeout_count – Type: uint32, Range: [0 to 2³² - 1]

Returns the timeout count for the different communication methods.

The methods 0-2 are available for all Bricks, 3-7 only for Master Bricks.

This function is mostly used for debugging during development, in normal operation the counters should nearly always stay at 0.

New in version 2.3.4 (Firmware).

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

For communication_method:

0 = None
1 = USB
2 = SPI Stack
3 = Chibi
4 = RS485
5 = WIFI
6 = Ethernet
7 = WIFI V2

BrickStepper.set_spitfp_baudrate¶

Function ID:	234
Request:	bricklet_port – Type: char, Range: ['a' to 'b'] baudrate – Type: uint32, Unit: 1 Bd, Range: [400000 to 2000000], Default: 1400000
Response:	no response

Sets the baudrate for a specific Bricklet port.

If you want to increase the throughput of Bricklets you can increase the baudrate. If you get a high error count because of high interference (see get_spitfp_error_count) you can decrease the baudrate.

If the dynamic baudrate feature is enabled, the baudrate set by this function corresponds to the maximum baudrate (see set_spitfp_baudrate_config).

Regulatory testing is done with the default baudrate. If CE compatibility or similar is necessary in your applications we recommend to not change the baudrate.

New in version 2.3.3 (Firmware).

BrickStepper.get_spitfp_baudrate¶

Function ID:	235
Request:	bricklet_port – Type: char, Range: ['a' to 'b']
Response:	baudrate – Type: uint32, Unit: 1 Bd, Range: [400000 to 2000000], Default: 1400000

Returns the baudrate for a given Bricklet port, see set_spitfp_baudrate.

New in version 2.3.3 (Firmware).

BrickStepper.get_spitfp_error_count¶

Function ID:	237
Request:	bricklet_port – Type: char, Range: ['a' to 'b']
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 Brick side. All Bricklets have a similar function that returns the errors on the Bricklet side.

New in version 2.3.3 (Firmware).

BrickStepper.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).

BrickStepper.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).

BrickStepper.is_status_led_enabled¶

Function ID:	240
Request:	empty payload
Response:	enabled – Type: bool, Default: true

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

New in version 2.3.1 (Firmware).

BrickStepper.get_chip_temperature¶

Function ID:	242
Request:	empty payload
Response:	temperature – Type: int16, Unit: 1/10 °C, Range: [-2¹⁵ to 2¹⁵ - 1]

Returns the temperature 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.

BrickStepper.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!

BrickStepper.get_identity¶

Function ID:	255
Request:	empty payload
Response:	uid – Type: char[8] connected_uid – Type: char[8] position – Type: char, Range: ['0' to '8'] hardware_version – Type: uint8[3] 0: major – Type: uint8, Range: [0 to 255] 1: minor – Type: uint8, Range: [0 to 255] 2: revision – Type: uint8, Range: [0 to 255] firmware_version – Type: uint8[3] 0: major – Type: uint8, Range: [0 to 255] 1: minor – Type: uint8, Range: [0 to 255] 2: revision – Type: uint8, Range: [0 to 255] device_identifier – Type: uint16, Range: [0 to 2¹⁶ - 1]

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 is the position in the stack from '0' (bottom) to '8' (top).

The device identifier numbers can be found here.

Callback Configuration Functions¶

BrickStepper.set_minimum_voltage¶

Function ID:	29
Request:	voltage – Type: uint16, Unit: 1 mV, Range: [0 to 2¹⁶ - 1], Default: 8000
Response:	no response

Sets the minimum voltage, below which the CALLBACK_UNDER_VOLTAGE callback is triggered. The minimum possible value that works with the Stepper Brick is 8V. You can use this function to detect the discharge of a battery that is used to drive the stepper motor. If you have a fixed power supply, you likely do not need this functionality.

BrickStepper.get_minimum_voltage¶

Function ID:	30
Request:	empty payload
Response:	voltage – Type: uint16, Unit: 1 mV, Range: [0 to 2¹⁶ - 1], Default: 8000

Returns the minimum voltage as set by set_minimum_voltage.

BrickStepper.set_all_data_period¶

Function ID:	38
Request:	period – Type: uint32, Unit: 1 ms, Range: [0 to 2³² - 1], Default: 0
Response:	no response

Sets the period with which the CALLBACK_ALL_DATA callback is triggered periodically. A value of 0 turns the callback off.

BrickStepper.get_all_data_period¶

Function ID:	39
Request:	empty payload
Response:	period – Type: uint32, Unit: 1 ms, Range: [0 to 2³² - 1], Default: 0

Returns the period as set by set_all_data_period.

Callbacks¶

BrickStepper.CALLBACK_UNDER_VOLTAGE¶

Function ID:	31
Response:	voltage – Type: uint16, Unit: 1 mV, Range: [0 to 2¹⁶ - 1]

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

BrickStepper.CALLBACK_POSITION_REACHED¶

Function ID:	32
Response:	position – Type: int32, Range: [-2³¹ to 2³¹ - 1]

This callback is triggered when a position set by set_steps or set_target_position is reached.

Note

Since we can't get any feedback from the stepper motor, this only works if the acceleration (see set_speed_ramping) 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.

BrickStepper.CALLBACK_ALL_DATA¶

Function ID:

Response:

current_velocity – Type: uint16, Unit: 1 1/s, Range: [0 to 2¹⁶ - 1]
current_position – Type: int32, Range: [-2³¹ to 2³¹ - 1]
remaining_steps – Type: int32, Range: [-2³¹ to 2³¹ - 1]
stack_voltage – Type: uint16, Unit: 1 mV, Range: [0 to 2¹⁶ - 1]
external_voltage – Type: uint16, Unit: 1 mV, Range: [0 to 2¹⁶ - 1]
current_consumption – Type: uint16, Unit: 1 mA, Range: [0 to 2¹⁶ - 1]

This callback is triggered periodically with the period that is set by set_all_data_period. The response values are: the current velocity, the current position, the remaining steps, the stack voltage, the external voltage and the current consumption of the stepper motor.

BrickStepper.CALLBACK_NEW_STATE¶

Function ID:	41
Response:	state_new – Type: uint8, Range: See meanings state_previous – Type: uint8, Range: See meanings

This callback is triggered whenever the Stepper Brick enters a new state. It returns the new state as well as the previous state.

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

For state_new:

1 = Stop
2 = Acceleration
3 = Run
4 = Deacceleration
5 = Direction Change To Forward
6 = Direction Change To Backward

For state_previous:

1 = Stop
2 = Acceleration
3 = Run
4 = Deacceleration
5 = Direction Change To Forward
6 = Direction Change To Backward

Internal Functions¶

Internal functions are used for maintenance tasks such as flashing a new firmware of changing the UID of a Bricklet. These task should be performed using Brick Viewer instead of using the internal functions directly.

BrickStepper.get_protocol1_bricklet_name¶

Function ID:	241
Request:	port – Type: char, Range: ['a' to 'b']
Response:	protocol_version – Type: uint8, Range: [0 to 255] firmware_version – Type: uint8[3] 0: major – Type: uint8, Range: [0 to 255] 1: minor – Type: uint8, Range: [0 to 255] 2: revision – Type: uint8, Range: [0 to 255] name – Type: 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.

BrickStepper.write_bricklet_plugin¶

Function ID:	246
Request:	port – Type: char, Range: ['a' to 'b'] offset – Type: uint8, Range: [0 to 255] chunk – Type: uint8[32], Range: [0 to 255]
Response:	no response

Writes 32 bytes of firmware to the bricklet attached at the given port. The bytes are written to the position offset * 32.

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

BrickStepper.read_bricklet_plugin¶

Function ID:	247
Request:	port – Type: char, Range: ['a' to 'b'] offset – Type: uint8, Range: [0 to 255]
Response:	chunk – Type: uint8[32], Range: [0 to 255]

Reads 32 bytes of firmware from the bricklet attached at the given port. The bytes are read starting at the position offset * 32.

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