basic PCF8574 functionality

Author: Sylvan Butler

Adafruit_GPIO/PCF8574.py

@@ -0,0 +1,101 @@
+'''
+Adafruit compatible using BaseGPIO class to represent a PCF8574/A IO expander
+Copyright (C) 2015 Sylvan Butler
+
+Permission is hereby granted, free of charge, to any person obtaining a copy of this software and
+associated documentation files (the "Software"), to deal in the Software without restriction,
+including without limitation the rights to use, copy, modify, merge, publish, distribute,
+sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all copies or substantial
+portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT
+LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
+IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
+WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
+SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+'''
+
+import Adafruit_GPIO as GPIO
+import Adafruit_GPIO.I2C as I2C
+
+
+
+IN = GPIO.IN
+OUT = GPIO.OUT
+HIGH = GPIO.HIGH
+LOW = GPIO.LOW
+
+
+class PCF8574(GPIO.BaseGPIO):
+    """Class to represent a PCF8574 or PCF8574A GPIO extender. Compatible
+    with the Adafruit_GPIO BaseGPIO class so it can be used as a custom GPIO
+    class for interacting with device.
+    """
+
+    NUM_GPIO = 8
+
+    def __init__(self, address, i2c=None, **kwargs):
+        address = int(address)
+        self.__name__ = \
+            "PCF8574" if address in range(0x20, 0x28) else \
+            "PCF8574A" if address in range(0x38, 0x40) else \
+            "Bad address for PCF8574(A): 0x%02X not in range [0x20..0x27, 0x38..0x3F]" % address
+        if self.__name__[0] != 'P':
+            raise ValueError(self.__name__)
+        # Create I2C device.
+        if i2c is None:
+            i2c = I2C
+        self._device = i2c.get_i2c_device(address, **kwargs)
+        # Buffer register values so they can be changed without reading.
+        self.iodir = 0xFF  # Default direction to all inputs is in
+        self.gpio = 0x00
+        self._write_pins()
+
+
+    def _write_pins(self):
+        self._device.writeRaw8(self.gpio | self.iodir)
+
+    def _read_pins(self):
+        return self._device.readRaw8() & self.iodir
+
+    def _validate_pin(self, pin):
+        # Raise an exception if pin is outside the range of allowed values.
+        if pin < 0 or pin >= self.NUM_GPIO:
+            raise ValueError('Invalid GPIO value, must be between 0 and {0}.'.format(self.NUM_GPIO))
+
+    def _bit2(self, src, bit, val):
+        bit = 1 << bit
+        return (src | bit) if val else (src & ~bit)
+
+
+    def setup(self, pin, mode):
+        self.setup_pins({pin: mode})
+
+    def setup_pins(self, pins):
+        if False in [y for x,y in [(self._validate_pin(pin),mode in (IN,OUT)) for pin,mode in pins.iteritems()]]:
+            raise ValueError('Invalid MODE, IN or OUT')
+        for pin,mode in pins.iteritems():
+            self.iodir = self._bit2(self.iodir, pin, mode)
+        self._write_pins()
+
+
+    def output(self, pin, value):
+        self.output_pins({pin: value})
+
+    def output_pins(self, pins):
+        [self._validate_pin(pin) for pin in pins.keys()]
+        for pin,value in pins.iteritems():
+            self.gpio = self._bit2(self.gpio, pin, bool(value))
+        self._write_pins()
+
+
+    def input(self, pin):
+        return self.input_pins([pin])[0]
+
+    def input_pins(self, pins):
+        [self._validate_pin(pin) for pin in pins]
+        inp = self._read_pins()
+        return [bool(inp & pin) for pin in pins]