import board      # Access Raspberry Pi Pico GPIO pins
import digitalio  # Control digital input/output pins
import time       # Used for delay and debounce timing

# ==============================================
# KEYPAD INPUT SETUP (MM74C922 ENCODER)
# ==============================================

# Data Available pin (signals when key is pressed)
data_available = digitalio.DigitalInOut(board.GP14)
data_available.direction = digitalio.Direction.INPUT   # Set as input

# Keypad data lines (D3D0), A,B,C,D
data_pins = [board.GP13, board.GP12, board.GP11, board.GP10]

data_inputs = []  # Store input pin objects

# Convert GPIO pins into digital input objects
for pin in data_pins:
    dio = digitalio.DigitalInOut(pin)   # Create digital input
    dio.direction = digitalio.Direction.INPUT   # Set as input
    data_inputs.append(dio)             # Add to list

# Keypad mapping (binary value character) #MM74C922 datasheet
keypad_map = {
    12: '?', 13: '?', 14: '?', 15: '?',
    8: '?', 9: '?', 10: '?', 11: '?',
    4: '?', 5: '?', 6: '?', 7: '?',
    0: '?', 1: '?', 2: '?', 3: '?'
}

# =================================================
# FUNCTION: READ KEYPAD
# =================================================
def read_keypad():

    # Check if keypad has sent data
    if data_available.value:

        value = 0 # Store 4-bit binary value

        # Convert 4 input bits into a number
        for i, pin in enumerate (data_inputs):
            if pin.value:
                value = (1 << (3 - i)) # Build binary number (D3+D0)

        return value # Return raw keypad value

    return None # No key pressed

# ====================================================
# CD4511 BCD OUTPUT (7-SEGMENT DISPLAY)
# ====================================================
A = digitalio.DigitalInOut (board.GP5) # BCD bit 0
B = digitalio.DigitalInOut (board.GP4) # BCD bit 1
C = digitalio.DigitalInOut (board.GP3) # BCD bit 2
D = digitalio.DigitalInOut (board.GP2) # BCD bit 3

# Set all BCD pins as OUTPUT
for pin in [A, B, C, D]:
    pin.direction = digitalio.Direction.OUTPUT

data_pins = [A, B, C, D] # Store BCD output pins

# ====================================
# LATCH CONTROL PINS
# ====================================

s72 = digitalio.DigitalInOut(board.GP7) # Controls tens display
s72.direction = digitalio. Direction.OUTPUT
s71 = digitalio.DigitalInOut(board.GP6) # Controls ones display
s71.direction = digitalio.Direction.OUTPUT

# ====================================================
# FUNCTION: SEND BCD TO DISPLAY
# ====================================================
def send_bcd(value):

    # Send 4-bit binary value to CD4511
    for i in range(4):
        data_pins[i].value = (value >> i) & 1

# ====================================================
# FUNCTION: LATCH DATA TO DISPLAY
# ====================================================
def latch(pin):

    pin.value = 0     # Enable latch (active low)
    time.sleep(0.001) # Small delay for hardware stability
    pin.value = 1     # Disable latch

# ====================================================
# MAIN TEST LOOP
# ====================================================
while True:

    bcd_val = read_keypad() # Read keypad binary value

    if bcd_val is not None: # If key is pressed

        # Convert binary value to readable key
        key = keypad_map.get(bcd_val, '?')

        print("Key Pressed:", key) # Show on Thonny Shell

    # Only send numeric keys (0-9) to CD4511
    if key.isdigit():
        
        send_bcd(int(key)) # Send number to 7-segment

    # Wait until key is released (debounce handling)
    while data_available.value:
        pass

    time.sleep(0.05) # Small delay to avoid bouncing