added notes to the README.md about I2C to 1602

Since this is a modified 1602 LCD display module designed to be used with I2C, there are differences in how this component is used versus a standard 1602 LCD display module.

project10/README.md

@@ -18,3 +18,36 @@ through the parallel data pins connected between the PCF8574 and the 1602.
 ### Raspberry Pi configuration changes
 
 The I2C subsystem of Raspbian on the Raspberry Pi must be turned on.
+
+## Notes about the 1602 LCD display of the kit
+
+The bare bones 1602 LCD display has the 8 data pins which are used to send both text
+data characters as well as hexadecimal commands to the 1602 LCD component. The hex
+commands specify how the 1602 LCD is to display the text characters.
+
+There are three control signal pins that are also used: R/W to signal read data
+or write data, EN to latch data, and RS to select whether data being sent is a
+command or a text character.
+
+Since the 1602 LCD display module of the Osoyoo Raspberry Pi Starter Kit is a modified
+module composed of a 1602 LCD display and a PCF8574 IC and we are using the I2C functionality
+rather than the raw 1602 LCD pins, the software interface is a bit different than a
+standard, unadorned 1602 LCD display module.
+
+The difference is that the I2C interface must also allow us to set the control signal pins
+as well as to send data/command bits. This is done by dividing the 8 bit serial character
+sent vis I2C to the PCF8574 IC into two nibbles. The high nibble indicates the control pin
+settings and the lower nibble indicates four bits of the 8 bit character being sent.
+
+This means that to send an 8 bit text character or an 8 bit command character requires two
+I2C writes, the first write to send the high order bits (bits 7 through 4) followed by a
+second write to send the low order bits (bits 3 through 0).
+
+See [16X2 LCD programming for beginners. Made easy](https://embeddedlifehelp.blogspot.com/2012/03/16x2-lcd-programming-for-beginners-made.html).
+
+See [lcd commands and understanding of LCD module](http://www.firmcodes.com/microcontrollers/8051-3/interfacing-lcd-with-8051/lcd-commands-and-understanding-of-lcd/).
+
+See [LCD - Liquid Crystal Display tutorial](http://www.microcontrollerboard.com/lcd.html) which describes 
+in greater detail what seems to be the actual 1602 LCD display module in the Osoyoo kit.
+
+See [Serial LCD quickstart](https://www.sparkfun.com/tutorials/246) which also seems to be similar to what is in the Osoyoo kit.