bitbangio – Digital protocols implemented by the CPU

The bitbangio module contains classes to provide digital bus protocol support regardless of whether the underlying hardware exists to use the protocol.

First try to use busio module instead which may utilize peripheral hardware to implement the protocols. Native implementations will be faster than bitbanged versions and have more capabilities.

All classes change hardware state and should be deinitialized when they are no longer needed if the program continues after use. To do so, either call deinit() or use a context manager. See Lifetime and ContextManagers for more info.

For example:

import bitbangio
from board import *

i2c = bitbangio.I2C(SCL, SDA)
print(i2c.scan())
i2c.deinit()

This example will initialize the the device, run scan() and then deinit() the hardware. The last step is optional because CircuitPython automatically resets hardware after a program finishes.

class bitbangio.I2C(scl: microcontroller.Pin, sda: microcontroller.Pin, *, frequency: int = 400000, timeout: int = 255)

Two wire serial protocol

I2C is a two-wire protocol for communicating between devices. At the physical level it consists of 2 wires: SCL and SDA, the clock and data lines respectively.

See also

Using this class directly requires careful lock management. Instead, use I2CDevice to manage locks.

See also

Using this class to directly read registers requires manual bit unpacking. Instead, use an existing driver or make one with Register data descriptors.

Parameters:
  • scl (Pin) – The clock pin
  • sda (Pin) – The data pin
  • frequency (int) – The clock frequency of the bus
  • timeout (int) – The maximum clock stretching timeout in microseconds
deinit(self)

Releases control of the underlying hardware so other classes can use it.

__enter__(self)

No-op used in Context Managers.

__exit__(self)

Automatically deinitializes the hardware on context exit. See Lifetime and ContextManagers for more info.

scan(self)

Scan all I2C addresses between 0x08 and 0x77 inclusive and return a list of those that respond. A device responds if it pulls the SDA line low after its address (including a read bit) is sent on the bus.

try_lock(self)

Attempts to grab the I2C lock. Returns True on success.

unlock(self)

Releases the I2C lock.

readfrom_into(self, address: int, buffer: WriteableBuffer, *, start: int = 0, end: Optional[int] = None)

Read into buffer from the device selected by address. The number of bytes read will be the length of buffer. At least one byte must be read.

If start or end is provided, then the buffer will be sliced as if buffer[start:end]. This will not cause an allocation like buf[start:end] will so it saves memory.

Parameters:
  • address (int) – 7-bit device address
  • buffer (WriteableBuffer) – buffer to write into
  • start (int) – Index to start writing at
  • end (int) – Index to write up to but not include
writeto(self, address: int, buffer: ReadableBuffer, *, start: int = 0, end: Optional[int] = None, stop: bool = True)

Write the bytes from buffer to the device selected by address and then transmits a stop bit. Use writeto_then_readfrom when needing a write, no stop and repeated start before a read.

If start or end is provided, then the buffer will be sliced as if buffer[start:end]. This will not cause an allocation like buffer[start:end] will so it saves memory.

Writing a buffer or slice of length zero is permitted, as it can be used to poll for the existence of a device.

Parameters:
  • address (int) – 7-bit device address
  • buffer (ReadableBuffer) – buffer containing the bytes to write
  • start (int) – Index to start writing from
  • end (int) – Index to read up to but not include
writeto_then_readfrom(self, address: int, out_buffer: ReadableBuffer, in_buffer: ReadableBuffer, *, out_start: int = 0, out_end: Optional[int] = None, in_start: int = 0, in_end: Optional[int] = None)

Write the bytes from out_buffer to the device selected by address, generate no stop bit, generate a repeated start and read into in_buffer. out_buffer and in_buffer can be the same buffer because they are used sequentially.

If start or end is provided, then the corresponding buffer will be sliced as if buffer[start:end]. This will not cause an allocation like buf[start:end] will so it saves memory.

Parameters:
  • address (int) – 7-bit device address
  • out_buffer (ReadableBuffer) – buffer containing the bytes to write
  • in_buffer (WriteableBuffer) – buffer to write into
  • out_start (int) – Index to start writing from
  • out_end (int) – Index to read up to but not include. Defaults to len(buffer)
  • in_start (int) – Index to start writing at
  • in_end (int) – Index to write up to but not include. Defaults to len(buffer)
class bitbangio.OneWire(pin: microcontroller.Pin)

Lowest-level of the Maxim OneWire protocol

OneWire implements the timing-sensitive foundation of the Maxim (formerly Dallas Semi) OneWire protocol.

Protocol definition is here: https://www.maximintegrated.com/en/app-notes/index.mvp/id/126

Create a OneWire object associated with the given pin. The object implements the lowest level timing-sensitive bits of the protocol.

Parameters:pin (Pin) – Pin to read pulses from.

Read a short series of pulses:

import bitbangio
import board

onewire = bitbangio.OneWire(board.D7)
onewire.reset()
onewire.write_bit(True)
onewire.write_bit(False)
print(onewire.read_bit())
deinit(self)

Deinitialize the OneWire bus and release any hardware resources for reuse.

__enter__(self)

No-op used by Context Managers.

__exit__(self)

Automatically deinitializes the hardware when exiting a context. See Lifetime and ContextManagers for more info.

reset(self)

Reset the OneWire bus

read_bit(self)

Read in a bit

Returns:bit state read
Return type:bool
write_bit(self, value: bool)

Write out a bit based on value.

class bitbangio.SPI(clock: microcontroller.Pin, MOSI: Optional[microcontroller.Pin] = None, MISO: Optional[microcontroller.Pin] = None)

A 3-4 wire serial protocol

SPI is a serial protocol that has exclusive pins for data in and out of the main device. It is typically faster than I2C because a separate pin is used to select a device rather than a transmitted address. This class only manages three of the four SPI lines: clock, MOSI, MISO. Its up to the client to manage the appropriate select line, often abbreviated CS or SS. (This is common because multiple secondaries can share the clock, MOSI and MISO lines and therefore the hardware.)

Construct an SPI object on the given pins.

See also

Using this class directly requires careful lock management. Instead, use SPIDevice to manage locks.

See also

Using this class to directly read registers requires manual bit unpacking. Instead, use an existing driver or make one with Register data descriptors.

Parameters:
  • clock (Pin) – the pin to use for the clock.
  • MOSI (Pin) – the Main Out Selected In pin.
  • MISO (Pin) – the Main In Selected Out pin.
deinit(self)

Turn off the SPI bus.

__enter__(self)

No-op used by Context Managers.

__exit__(self)

Automatically deinitializes the hardware when exiting a context. See Lifetime and ContextManagers for more info.

configure(self, *, baudrate: int = 100000, polarity: int = 0, phase: int = 0, bits: int = 8)

Configures the SPI bus. Only valid when locked.

Parameters:
  • baudrate (int) – the clock rate in Hertz
  • polarity (int) – the base state of the clock line (0 or 1)
  • phase (int) – the edge of the clock that data is captured. First (0) or second (1). Rising or falling depends on clock polarity.
  • bits (int) – the number of bits per word
try_lock(self)

Attempts to grab the SPI lock. Returns True on success.

Returns:True when lock has been grabbed
Return type:bool
unlock(self)

Releases the SPI lock.

write(self, buf: ReadableBuffer)

Write the data contained in buf. Requires the SPI being locked. If the buffer is empty, nothing happens.

readinto(self, buf: WriteableBuffer)

Read into the buffer specified by buf while writing zeroes. Requires the SPI being locked. If the number of bytes to read is 0, nothing happens.

write_readinto(self, buffer_out: ReadableBuffer, buffer_in: WriteableBuffer, *, out_start: int = 0, out_end: Optional[int] = None, in_start: int = 0, in_end: Optional[int] = None)

Write out the data in buffer_out while simultaneously reading data into buffer_in. The lengths of the slices defined by buffer_out[out_start:out_end] and buffer_in[in_start:in_end] must be equal. If buffer slice lengths are both 0, nothing happens.

Parameters:
  • buffer_out (ReadableBuffer) – Write out the data in this buffer
  • buffer_in (WriteableBuffer) – Read data into this buffer
  • out_start (int) – Start of the slice of buffer_out to write out: buffer_out[out_start:out_end]
  • out_end (int) – End of the slice; this index is not included. Defaults to len(buffer_out)
  • in_start (int) – Start of the slice of buffer_in to read into: buffer_in[in_start:in_end]
  • in_end (int) – End of the slice; this index is not included. Defaults to len(buffer_in)