- HD44780 LCD SUPPORT -

Support for the HD44780 LCD is via the wiringPi library available at
http://wiringpi.com/download-and-install/ which must be installed in all cases.

The HD44780 in 4-bit mode is probably the most common connection method and
wiring details can be found at http://wiringpi.com/dev-lib/lcd-library/

The setup that is commonly used for MMDVM is the 4-bit connection that is also
documented within wiringPi. The HD44780 displays have a standardized 16-pin
connector (14 pins if without backlight). The pin numbers on HD44780 refer to
this standard numbering.

The pin numbers on Raspberry Pi side are the physical pin numbers of the GPIO
pin header, in brackets the wiringPi pin number as these are referred to in the
MMDVM.ini file.

The wiring ist as follows:

 HD44780 pin    Raspberry Pi GPIO
  GND  1  --------   6 GND
  VCC  2  --------   2 +5V
  V0   3  --------     Trimmer between +5V and GND for contrast
  RS   4  --------  26 CE1 (11)
  RW   5  --------   6 GND
  E    6  --------  24 CE0 (10)
  D0   7
  D1   8
  D2   9
  D3  10
  D4  11  --------  11 GPIO0 (0)
  D5  12  --------  12 GPIO1 (1)
  D6  13  --------  13 GPIO2 (2)
  D7  14  --------  15 GPIO3 (3)
  VCC 15  --------   2 +5V
  GND 16  --------   6 GND

The relevant part in the MMDVM.ini is like outlined below.

[HD44780]
Rows=4
Columns=20

# For basic HD44780 displays (4-bit connection)
# rs, strb, d0, d1, d2, d3
Pins=11,10,0,1,2,3

To compile MMDVMHost with support for the HD44780 use the following commands.

# make clean
# make -f Makefile.Pi.HD44780

Other HD44780 variations exist that connect via I2C. Support is also via 
wiringPi, but to compile for each I2C device requires a different Makefile 
depending on the IC attached to the LCD.

                           - ADAFRUIT RGB LCD SHIELD -

The Adafruit RGB LCD Shield is available from https://www.adafruit.com/product/714
I2C is  via the MCP23017 IC and is enabled with Makefile.Pi.Adafruit. The 
I2C device address in MMDVM.ini should be set to 0x20.

                                 - PCF8574 IC -

HD44780 LCDs connected via a PCF8574 Remote 8-Bit I/O Expander are available on
eBay for very little money! This IC uses Makefile.Pi.PCF8574 and the I2C
device address should be set to 0x27.

                                   - BEWARE -

        The I2C device address can be manually configured on some devices! 

                       - CHECK YOUR ACTUAL DEVICE ADDRESS -

More information on configuring and using I2C on the RPi including how to probe
the I2C bus for device addresses can be found at
https://learn.sparkfun.com/tutorials/raspberry-pi-spi-and-i2c-tutorial#i2c-on-pi

                             - PWM BACKLIGHT CONTROL - 

Whilst connected in 4-bit mode or via the PCF8574 IC, the LED backlight can be
wired for control via PWM.  Connect the backlight +ve pin to any spare GPIO pin 
and configure MMDVM.ini as appropriate. By default, wiringPi pin 21 is 
configured.