Adafruit_CircuitPython_74HC595: Added support for multiple shift registers

adafruit_74hc595.py

@@ -44,6 +44,8 @@ def __init__(self, pin_number, shift_register_74hc595):
         ShiftRegister74HC595 instance.
         """
         self._pin = pin_number
+        self._byte_pos = self._pin // 8
+        self._byte_pin = self._pin % 8
         self._shift_register = shift_register_74hc595
 
     # kwargs in switch functions below are _necessary_ for compatibility
@@ -65,16 +67,23 @@ def switch_to_input(self, **kwargs):  # pylint: disable=no-self-use
     @property
     def value(self):
         """The value of the pin, either True for high or False for low."""
-        return self._shift_register.gpio & (1 << self._pin) == (1 << self._pin)
+        return self._shift_register.gpio[self._byte_pos] & (1 << self._byte_pin) == (
+            1 << self._byte_pin
+        )
 
     @value.setter
     def value(self, val):
-        gpio = self._shift_register.gpio
-        if val:
-            gpio |= 1 << self._pin
-        else:
-            gpio &= ~(1 << self._pin)
-        self._shift_register.gpio = gpio
+
+        if (
+            self._pin >= 0
+            and self._pin < self._shift_register.number_of_shift_registers * 8
+        ):
+            gpio = self._shift_register.gpio
+            if val:
+                gpio[self._byte_pos] |= 1 << self._byte_pin
+            else:
+                gpio[self._byte_pos] &= ~(1 << self._byte_pin)
+            self._shift_register.gpio = gpio
 
     @property
     def direction(self):
@@ -100,23 +109,31 @@ def pull(self, val):  # pylint: disable=no-self-use
 
 
 class ShiftRegister74HC595:
-    """Initialise the 74HC595 on specified SPI bus."""
+    """Initialise the 74HC595 on specified SPI bus
+    and indicate the number of shift registers being used
+    """
 
-    def __init__(self, spi, latch):
+    def __init__(self, spi, latch, number_of_shift_registers=1):
         self._device = spi_device.SPIDevice(spi, latch, baudrate=1000000)
-        self._gpio = bytearray(1)
-        self._gpio[0] = 0x00
+        self._number_of_shift_registers = number_of_shift_registers
+        self._gpio = bytearray(self._number_of_shift_registers)
+
+    @property
+    def number_of_shift_registers(self):
+        """The number of shift register chips """
+        return self._number_of_shift_registers
 
     @property
     def gpio(self):
         """The raw GPIO output register.  Each bit represents the
         output value of the associated pin (0 = low, 1 = high).
         """
-        return self._gpio[0]
+        return self._gpio
 
     @gpio.setter
     def gpio(self, val):
-        self._gpio[0] = val & 0xFF
+        self._gpio = val
+
         with self._device as spi:
             # pylint: disable=no-member
             spi.write(self._gpio)
@@ -125,5 +142,5 @@ def get_pin(self, pin):
         """Convenience function to create an instance of the DigitalInOut class
         pointing at the specified pin of this 74HC595 device .
         """
-        assert 0 <= pin <= 7
+        assert 0 <= pin <= (self._number_of_shift_registers * 8) - 1
         return DigitalInOut(pin, self)