PIC Tutorial - LCD Board

LCD Board

LCD Pin Functions
Pin Function Description
1 Vss Ground
2 Vdd +ve supply
3 Vee Contrast
4 RS Register Select
5 R/W Read/Write
6 E Enable
7 D0 Data bit 0 (8 bit)
8 D1 Data bit 1 (8 bit)
9 D2 Data bit 2 (8 bit)
10 D3 Data bit 3 (8 bit)
11 D4 Data bit 4
12 D5 Data bit 5
13 D6 Data bit 6
14 D7 Data bit 7

 

 

 

 

 

 

 

This is the LCD Board, using an LCD module based on the industry standard Hitachi HD44780, it connects to 7 pins of one port, and operates in 4 bit 'nibble' mode to save I/O pins. By connecting to PortA we have to use a pull-up resistor (R1) on RA4, and are unable to use RA5 (which is only an input), however this frees all of PortB which will allow us to use some of the extra hardware available on PortB, along with the LCD, in a later tutorial. The potentiometer P1, is for adjusting the contrast of the display, and if incorrectly adjusted can cause the display to be invisible. Although it's labelled as connecting to PortA, as with most of the boards, it can also be connected to PortB if required. By using 4 bit mode we can connect the entire LCD module to one port, it uses exactly 10 pins (just right for our Molex connectors). In 4 bit mode we don't use pins 7-10, which are used as the lower 4 data bits in 8 bit mode, instead we write (or read) to the upper 4 pins twice, transferring half of the data each time - this makes the program slightly more complicated, but is well worth it for the pins saved - particularly as it allows us to use just the one 10 pin connector.

This is the top view of the LCD board, the upper connector goes to the main processor board, and the lower one is where the LCD module plugs in - you could solder the wires from the LCD directly to the board, but I chose to use a Molex plug and socket - so I can plug different LCD's into the same board. The LCD module is wired as the circuit above, with pins 7-10 of the module being ignored and being in sequence from pin 1 to pin 14.
The bottom of the LCD board, the two track breaks are marked with blue circles, and it only has seven wire links on the top (there's a short one just above the preset). The vertically mounted preset resistor is for setting the contrast of the display.
Front and rear views of the wired 2x16 LCD module, I used about 3 inches of wire to the Molex socket, notice the four connections left blank in the middle, these are the extra pins used for 8 bit mode. Also notice the single blue wire to the socket, I've done this on all the leads I've made up - it signifies pin 1 of the connector.

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