text: # MicroPython SSD1306 OLED driver using I2C interface
  #
  # library taken from repository at:
  # https://github.com/micropython/micropython/blob/master/drivers/display/ssd1306.py
  #
  from micropython import const
  import framebuf
  
  # register definitions
  SET_CONTRAST = const(0x81)
  SET_ENTIRE_ON = const(0xA4)
  SET_NORM_INV = const(0xA6)
  SET_DISP = const(0xAE)
  SET_MEM_ADDR = const(0x20)
  SET_COL_ADDR = const(0x21)
  SET_PAGE_ADDR = const(0x22)
  SET_DISP_START_LINE = const(0x40)
  SET_SEG_REMAP = const(0xA0)
  SET_MUX_RATIO = const(0xA8)
  SET_COM_OUT_DIR = const(0xC0)
  SET_DISP_OFFSET = const(0xD3)
  SET_COM_PIN_CFG = const(0xDA)
  SET_DISP_CLK_DIV = const(0xD5)
  SET_PRECHARGE = const(0xD9)
  SET_VCOM_DESEL = const(0xDB)
  SET_CHARGE_PUMP = const(0x8D)
  
  # Subclassing FrameBuffer provides support for graphics primitives
  # http://docs.micropython.org/en/latest/pyboard/library/framebuf.html
  class SSD1306(framebuf.FrameBuffer):
      def __init__(self, width, height, external_vcc):
          self.width = width
          self.height = height
          self.external_vcc = external_vcc
          self.pages = self.height // 8
          self.buffer = bytearray(self.pages * self.width)
          super().__init__(self.buffer, self.width, self.height, framebuf.MONO_VLSB)
          self.init_display()
  
      def init_display(self):
          for cmd in (
              SET_DISP | 0x00,  # off
              # address setting
              SET_MEM_ADDR,
              0x00,  # horizontal
              # resolution and layout
              SET_DISP_START_LINE | 0x00,
              SET_SEG_REMAP | 0x01,  # column addr 127 mapped to SEG0
              SET_MUX_RATIO,
              self.height - 1,
              SET_COM_OUT_DIR | 0x08,  # scan from COM[N] to COM0
              SET_DISP_OFFSET,
              0x00,
              SET_COM_PIN_CFG,
              0x02 if self.width > 2 * self.height else 0x12,
              # timing and driving scheme
              SET_DISP_CLK_DIV,
              0x80,
              SET_PRECHARGE,
              0x22 if self.external_vcc else 0xF1,
              SET_VCOM_DESEL,
              0x30,  # 0.83*Vcc
              # display
              SET_CONTRAST,
              0xFF,  # maximum
              SET_ENTIRE_ON,  # output follows RAM contents
              SET_NORM_INV,  # not inverted
              # charge pump
              SET_CHARGE_PUMP,
              0x10 if self.external_vcc else 0x14,
              SET_DISP | 0x01,
          ):  # on
              self.write_cmd(cmd)
          self.fill(0)
          self.show()
  
      def poweroff(self):
          self.write_cmd(SET_DISP | 0x00)
  
      def poweron(self):
          self.write_cmd(SET_DISP | 0x01)
  
      def contrast(self, contrast):
          self.write_cmd(SET_CONTRAST)
          self.write_cmd(contrast)
  
      def invert(self, invert):
          self.write_cmd(SET_NORM_INV | (invert & 1))
  
      def show(self):
          x0 = 0
          x1 = self.width - 1
          if self.width == 64:
              # displays with width of 64 pixels are shifted by 32
              x0 += 32
              x1 += 32
          self.write_cmd(SET_COL_ADDR)
          self.write_cmd(x0)
          self.write_cmd(x1)
          self.write_cmd(SET_PAGE_ADDR)
          self.write_cmd(0)
          self.write_cmd(self.pages - 1)
          self.write_data(self.buffer)
  
  
  class SSD1306_I2C(SSD1306):
      def __init__(self, width, height, i2c, addr=0x3C, external_vcc=False):
          self.i2c = i2c
          self.addr = addr
          self.temp = bytearray(2)
          self.write_list = [b"\x40", None]  # Co=0, D/C#=1
          super().__init__(width, height, external_vcc)
  
      def write_cmd(self, cmd):
          self.temp[0] = 0x80  # Co=1, D/C#=0
          self.temp[1] = cmd
          self.i2c.writeto(self.addr, self.temp)
  
      def write_data(self, buf):
          self.write_list[1] = buf
          self.i2c.writevto(self.addr, self.write_list)