Department of Electronic & Electrical Engineering LCD character display (parallel interface). How to interface a LCD character display to a PIC.

Department of Electronic & Electrical Engineering Applications Used in many devices which need a simple monochrome display:  FAX machines  Phones.  Industrial test equipment  Volt meters  Student projects ?  Etc...

Department of Electronic & Electrical Engineering Resources  Powertip PC1601A 1x16 LCD data sheet (not much help)  Hitachi HD44780 data sheet (lots of detail)   (recommended)  (I pinched this code)  lcd4bitHello.asm (my example code ) 

Department of Electronic & Electrical Engineering POWERTIP PC 1601A Schematic Showing the HD44780U and the LCD display HD44780 (another micro controller!)

Department of Electronic & Electrical Engineering Hitachi HD44780 LCD microcontroller The HD44780 is a dot-matrix LCD controller Lots of LCDs use this controller. It provides the functionality and memory to drive the LCD. It allows you to use simple interface to drive the display A single HD44780 can display one 8 characters line OR two 8 character lines one 16 character line (pretending to be 2 lines) Can be driven using just 6 connection to the PIC

Department of Electronic & Electrical Engineering PIN Descriptions VSS Power supply (GND) VCC Power supply (+5V) VEE Contrast adjust RS 0 = Instruction input 1 = Data input R/W 0 = Write to LCD module 1 = Read from LCD module EN Enable signal D0-7 Data bus lines 0-7

Department of Electronic & Electrical Engineering Connections (4 bit mode) RW can be set low because we will not be reading from device 4bit mode does not use D0-3

Department of Electronic & Electrical Engineering Sending data/instructions to the LCD Data sent to the LCD controller can be either an:  Instruction (if RS is high)  Data (character) (if RS is low) To send a value (Data/Instruction) to the LCD  Set RS appropriately  Put value onto lines D4-7  Strobe E (low high low)

Department of Electronic & Electrical Engineering LCD Instructions (RS high) --- examples:  Clear LCD  Position the cursor  Set direction of cursor  Set address of cursor  Set 4/8 bit mode  Set single / two line mode  More...

Department of Electronic & Electrical Engineering Display Data RAM (DDRAM) Characters are stored by the HD44780 in Display data RAM (DDRAM) This has a capacity of 80 characters (bytes). DD RAM address is the position of the cursor The DD RAM address layout for 2 line display is.

Department of Electronic & Electrical Engineering Initializing the device. If you are lucky the device will initialize itself on power up. However this will only happen if some conditions are met (e.g. time to go from zero to full power). It is best to do a full software reset.... makes sure the device is initialized properly.

Department of Electronic & Electrical Engineering Reset sequence of LCD (see lcd_init). Wait for about 20mS Send the first init value (0x30) Wait for about 10mS Send second init value (0x30) Wait for about 1mS Send third init value (0x30) Wait for 1mS Select bus width (0x20 for 4-bit) Wait for 1mS

Department of Electronic & Electrical Engineering 88bit version

Department of Electronic & Electrical Engineering Switching to 4 bit Mode We want to use 4bit mode. But controller starts in 8 bit mode! We can switch to 4bit mode by sending B' ' ; DL=0 sets 4 bit mode (note D0-3 can be zero).

Department of Electronic & Electrical Engineering 4 Bit mode  Once in 4 bit mode we can send an 8 bit instructions as 2 nibbles.  High nibble first.  See routine lcd_send_w in the example code

Department of Electronic & Electrical Engineering Writing characters to the LCD. Each character be represented by a byte of data Each location on the display has an address. The controller has a cursor (address of the next character to be written) We write a character to the display by Setting RS high Put character code on data lines Strobe E The cursor is moved ready for the next character.

Character codes.

Department of Electronic & Electrical Engineering Example program lcd4bitHello.asm Example that displays Hello on the LCD display. Initializes the LCD Clears the LCD Sends 'H' 'e' 'l' 'l' 'o'

Department of Electronic & Electrical Engineering Demo: lcd4bitHelloWorld.asm

Department of Electronic & Electrical Engineering Screen Configurations There are various LCD screen sizes. Common ones are 8X1 (one row of 8 characters) 16x1 16x2 20x2 20x4 The driver uses an address to define the position of a character. The location of an address on the display depends on the device. Some 16x1 devices behave differently from others!!!

Department of Electronic & Electrical Engineering The PC 1601A 16x1 LCD display From the controllers point of view it is a 2 line device. The first 8 characters are on line 1 The second 8 characters are on line 2 Each line can have 40 characters (only 8 displayed) There are display shift operations which use this feature.

Department of Electronic & Electrical Engineering Addresses of characters for PC 1601A The second 8 characters start at address 40!! This is because the connections to the controller are like a second line with 40 characters per line!!!!!

Department of Electronic & Electrical Engineering Solution to the exercise  To send characters to the second 8 locations  Send a instruction to set the cursor address to 40  Send more characters

Department of Electronic & Electrical Engineering Set cursor address instruction.

Department of Electronic & Electrical Engineering HD44780 driving a 2 line LCD

Department of Electronic & Electrical Engineering 2 rows mapped onto 1 row.