User manual

The LCD controller gives us two ways to send data: in one-byte (8 bit) chunks, or as two

consecutive nibbles (4 bit). The second approach seems more complicated, but very

frequently used. Why? It simplifies the hardware, and lets us talk to the LCD with half as

many data lines. In general, I/O lines are a scarce resource! We use the 4-bit method on

this board, and need only 6 I/O lines (2 control + 4 data) to communicate with the LCD.

Here are the digital I/O connections between our Pi and the LCD controller:

GPIO#

LCD Pin

Function

Enable

Bit 0 (Data line D4)

Bit 1 (Data line D5)

Bit 2 (Data line D6)

Bit 3 (Data line D7)

Now we have enough information to program our data lines on the Pi. We need to set up 6

GPIO lines as outputs. I like to give each line a name, rather than just a number

GPIO.setup(LCD_D4,GPIO.OUT)

GPIO.setup(LCD_D5,GPIO.OUT)

GPIO.setup(LCD_D6,GPIO.OUT)

…

If you want to, you can put all the output lines in a list, and then loop through them:

OUTPUTS = [LCD_RS, LCD_E, LCD_D4, LCD_D5, LCD_D6, LCD_D7]

for ioLine in OUTPUTS:

GPIO.setup(ioLine,GPIO.OUT)

3) NIBBLES & BYTES

Put on your thinking cap, because it’s time for the hard part: sending data to the LCD

controller. There are 8 bits to each byte, but we can only send 4 bits at a time. And we

have to time them according to the controller’s specifications. Check out the datasheet for

the specific details. The gist is to send the upper 4 bits of the data, toggle the enable pin,

and then send the lower 4 bits. The half-byte chunks are called nibbles.

def SendByte (data):

SendNibble(data) #send upper bits first

PulseEnableLine() #pulse the enable line

data = (data & 0x0F)<< 4 #shift 4 bits to left

SendNibble(data) #send lower bits now

PulseEnableLine() #pulse the enable line

def PulseEnableLine():

#Pulse the LCD Enable line; used for clocking in data

mSec = 0.0005 #use half-millisecond delay

time.sleep(mSec) #give time for inputs to settle

GPIO.output(LCD_E, GPIO.HIGH) #pulse E high