Alternatively, you can also drive the screen directly from the Raspberry Pi with the following connections:

We are not using the I²C bus here.

LCD	VSS	VDD	V0	RS	RW	E	DB4	DB5	DB6	DB7
LCD Pin	1	2	3	4	5	6	11	12	13	14
Raspberry Pi GPIO	6 (GND)	2 (5V)	Contrast	11	13 (GND)	15	12	16	18	22

The preceding table lists the connections required between the Raspberry Pi and the HD44780-compatible, alphanumeric display module.

The contrast pin (V0) can be connected to a variable resistor as before (with one side connected to the 5 V supply and the other to GND); although, depending on the screen, you may find you can connect directly to GND/5 V to obtain the maximum contrast.

The wiringpi2 LCD library assumes that the RW pin is connected to GND (read only); this avoids the risk that the LCD will send data back if it is connected directly to the Raspberry Pi (this would be a problem since the screen is powered by 5 V and will send data using 5 V logic).

Ensure that you update the code with the new AF_XX references and refer to the physical pin number by changing the setup within the gpiosetup() function. We can also skip the setup of the MCP23017 device.

Have a look at the following commands:

wiringpi2.wiringPiSetup()
wiringpi2.mcp23017Setup(AF_BASE,0x20)

Replace the preceding commands with the following command:

wiringpi.wiringPiSetupPhys()

You can see that we only need to change the pin references to switch between using the I/O expander and not using it, which shows how convenient the wiringpi2 implementation is.