[an error occurred while processing this directive]
[an error occurred while processing this directive]
[an error occurred while processing this directive]
How to control a HD44780-based Character-LCD
[an error occurred while processing this directive]
How to control a HD44780-based Character-LCD
The Industry Standard Character LCD
Visitor #
[an error occurred while processing this directive]
- HD44780-based (industry-standard) character-LCD, all software in this chapter is based on it's instruction-set.
- 8051 (or derivate) running on a 11.0952MHz crystal, some code is based on this frequency.
- 8-bit interface between microcontroller and LCD-module.
- All procedures coded as seperate .P51 programs so, when compiled and put in a library, only used procedures will be linked and loaded into (E)(E)(P)ROM.
- Can be (is) used as a 'device-driver'.
/* Necessairy global declarations in source file: */
DECLARE lcdregs BYTE PUBLIC AT (0....H) AUXILIARY;
DECLARE lcddata BYTE PUBLIC AT (0....H) AUXILIARY;
DECLARE lcdstat WORD PUBLIC;
DECLARE lcdsize BYTE PUBLIC;
/* 'lcdregs' and 'lcddata' form the interface to the display. */
/* must use the 'AT' attribute (hardware address decoding). */
/* 'lcdstat' and 'lcdsize' contain status information used by */
/* procedures in LCD.LIB and should not be changed by the user. */
- Global procedure declarations to get access to the library.
Code:
lcdinit:PROCEDURE(size) EXTERNAL;
DECLARE size BYTE;
END lcdinit;
lcdbusy:PROCEDURE BIT EXTERNAL;
END lcdbusy;
lcdclear:PROCEDURE EXTERNAL;
END lcdclear;
lcdhome:PROCEDURE EXTERNAL;
END lcdhome;
lcddmode:PROCEDURE(function) EXTERNAL;
DECLARE function BYTE;
END lcddmode;
lcdemode:PROCEDURE(function) EXTERNAL;
DECLARE function BYTE;
END lcdemode;
lcdsdda:PROCEDURE(ramaddress) EXTERNAL;
DECLARE ramaddress BYTE;
END lcdsdda;
lcdscga:PROCEDURE(ramaddress) EXTERNAL;
DECLARE ramaddress BYTE;
END lcdscga;
lcdgaddr:PROCEDURE BYTE EXTERNAL;
END lcdgaddr;
- Tests if the LCD is busy.
- Returnvalue (bit):
0 = LCD ready for instructions/data
1 = LCD busy
Code:
lcdbusy:DO;
DECLARE lcdregs BYTE EXTERNAL AUXILIARY;
lcdbusy:PROCEDURE BIT PUBLIC;
IF (lcdregs AND 080H) <> 0 /* test busy flag */
THEN /* LCD is busy */
RETURN (1);
ELSE /* LCD is ready */
RETURN (0);
END lcdbusy;
END lcdbusy;
- Clears display and returns cursor to home position (upper-left corner).
Code:
lcdclear:DO;
DECLARE lcdregs BYTE EXTERNAL AUXILIARY;
lcdbusy:PROCEDURE BIT EXTERNAL;
END lcdbusy;
lcdclear:PROCEDURE PUBLIC;
DO WHILE lcdbusy; /* wait till LCD ready */
END;
lcdregs = 001H; /* clear display, return home */
CALL TIME(30); /* wait since busy flag isn't supported */
/* while clearing the display */
END lcdclear;
END lcdclear;
- Returns cursor to home position.
- Returns display to original position (when shifted).
Code:
lcdhome:DO;
DECLARE lcdregs BYTE EXTERNAL AUXILIARY;
lcdbusy:PROCEDURE BIT EXTERNAL;
END lcdbusy;
lcdhome:PROCEDURE PUBLIC;
DO WHILE lcdbusy; /* wait till LCD ready */
END;
lcdregs = 02H; /* home display and cursor */
END lcdhome;
END lcdhome;
- Sets entry mode of the LCD
- b0 : 0 = no display shift, 1 = display shift
b1 : 0 = auto-decrement, 1 = auto-increment
b2-b7 : don't care
Code:
lcdemode:DO;
DECLARE lcdregs BYTE EXTERNAL AUXILIARY;
lcdbusy:PROCEDURE BIT EXTERNAL;
END lcdbusy;
lcdemode:PROCEDURE(function) PUBLIC;
DECLARE function BYTE;
function = (function AND 003H) + 004H; /* strip bits and set b2 */
DO WHILE lcdbusy; /* wait till LCD ready */
END;
lcdregs = function; /* set entry mode */
END lcdemode;
END lcdemode;
- Sets display control
- b0 : 0 = cursor blink off, 1 = cursor blink on (if b1 = 1)
b1 : 0 = cursor off, 1 = cursor on
b2 : 0 = display off, 1 = display on (display data remains in DD-RAM)
b3-b7 : don't care
Code:
lcddmode:DO;
DECLARE lcdregs BYTE EXTERNAL AUXILIARY;
lcdbusy:PROCEDURE BIT EXTERNAL;
END lcdbusy;
lcddmode:PROCEDURE(function) PUBLIC;
DECLARE function BYTE;
function = (function AND 007H) + 008H; /* strip bits and set b3 */
DO WHILE lcdbusy; /* wait till LCD ready */
END;
lcdregs = function; /* set display mode */
END lcddmode;
END lcddmode;
- Returns address counter contents, used for both DDRAM and CGRAM.
Code:
lcdgaddr:DO;
DECLARE lcdregs BYTE EXTERNAL AUXILIARY;
lcdbusy:PROCEDURE BIT EXTERNAL;
END lcdbusy;
lcdgaddr:PROCEDURE BYTE PUBLIC;
DO WHILE lcdbusy; /* wait till LCD ready */
END;
RETURN (lcdregs AND 07FH); /* get current address */
END lcdgaddr;
END lcdgaddr;
lcdwc:DO;
DECLARE lcddata BYTE EXTERNAL AUXILIARY;
lcdbusy:PROCEDURE BIT EXTERNAL;
END lcdbusy;
lcdwc:PROCEDURE(character) PUBLIC;
DECLARE character BYTE;
DO WHILE lcdbusy; /* wait till LCD ready */
END;
lcddata = character; /* write char. to LCD */
END lcdwc;
END lcdwc;
- Load a user-defined character definition into the HD44780 character generator memory.
Quick explanation on how to implement user-defined characters:
First you will need to make a pixel definition for the characters
you want to use. Below is the pixel definition for an underlined
'0' (char code 0x30) based on a 5x7 dots character definition:
| bits | byte
row | 76543210 | value
------------------------
000 | xxx | 0x0E
001 | x x | 0x11
010 | x xx | 0x13
011 | x x x | 0x15
100 | xx x | 0x19
101 | x x | 0x11
110 | xxx | 0x0E
111 | xxxxx | 0x1F
The byte values need to be loaded into CGRAM address 00cccrrr
(binary), where:
- ccc = user-defined character number (0..7)
- rrr = row number of the user-defined character (0..7)
Once that is done you can write user-defined character codes 0..7 to the
desired LCD character position, just like you do with 'normal' characters.
User-defined character definitions may be redefined 'on-the-fly'.
While defining a 5x7 dots character:
- Character code bits (DDRAM) 2..0 correspond to CGRAM address bits 5..3
(i.e. 8 possible user-defined characters).
While defining a 5x10 dots character:
- Character code bits (DDRAM) 2..1 correspond to CGRAM address bits 5..4
(i.e. 4 possible user-defined characters).
It is best to switch off the cursor while writing to CGRAM.
See also 2.6. Related pages.
- Function parameters:
charno : the character number (0..7) to be defined
sourceaddr : pointer to an 8-byte array in code memory which holds the character definition
Code:
lcduserchar:do;
declare lcdregs byte external auxiliary;
declare lcddata byte external auxiliary;
lcdgaddr:procedure byte external;
end lcdgaddr;
lcdbusy:procedure bit external;
end lcdbusy;
lcdsdda:procedure(ramaddress) external;
declare ramaddress byte;
end lcdsdda;
lcduserchar:procedure(charno,sourceaddr) public;
declare charno byte;
declare sourceaddr address;
declare pattern based sourceaddr byte constant;
declare ddrampos byte;
if charno >= 8
then /* invalid character number */
return; /* quit */
ddrampos = lcdgaddr; /* get current DDRAM position */
do while lcdbusy; /* wait till LCD ready */
end;
lcdregs = (charno * 8) + 040h; /* set new CGRAM address */
do charno = 0 to 7;
do while lcdbusy; /* wait till LCD ready */
end;
lcddata = pattern; /* write bit-pattern to LCD */
sourceaddr = sourceaddr + 1; /* point to next byte */
end;
call lcdsdda(ddrampos); /* restore DDRAM position */
end lcduserchar;
end lcduserchar;
- Sets the cursor on the desired row and character position.
- Function parameters:
row : 0-based row number
position : 0-based position (column)
Note: lcdsize.dcl contains the declarations mentioned in paragraph 3.1.2.2. Literal declarations.
Code:
lcdscp:DO;
$include(c:\plm51\lcdsize.dcl)
DECLARE lcdregs BYTE EXTERNAL AUXILIARY;
DECLARE lcdsize BYTE EXTERNAL;
lcdbusy:PROCEDURE BIT EXTERNAL;
END lcdbusy;
lcdscp:PROCEDURE(row,position) PUBLIC;
DECLARE row BYTE;
DECLARE position BYTE;
if lcdsize > lcd4x40
then /* unknown display size */
return;
/*----------------------- column positioning -------------------------------*/
do case lcdsize;
if position >= 8 /* 1 x 16 */
then
position = position + 040h;
; /* 2 x 16 */
; /* 4 x 16 */
if position >= 10 /* 1 x 20 */
then
position = position + 040h;
; /* 2 x 20 */
; /* 4 x 20 */
if position >= 12 /* 1 x 24 */
then
position = position + 040h;
; /* 2 x 24 */
; /* 4 x 24 */
if position >= 16 /* 1 x 32 */
then
position = position + 040h;
; /* 2 x 32 */
; /* 4 x 32 */
if position >= 20 /* 1 x 40 */
then
position = position + 040h;
; /* 2 x 40 */
; /* 4 x 40 */
end;
if (lcdsize = lcd2x16)
or (lcdsize = lcd2x20)
or (lcdsize = lcd2x24)
or (lcdsize = lcd2x32)
or (lcdsize = lcd2x40)
then
do case row;
; /* row 0 */
position = position + 040h; /* row 1 */
end;
if (lcdsize = lcd4x16)
or (lcdsize = lcd4x20)
then
do case row;
; /* row 0 */
position = position + 040h; /* row 1 */
position = position + 014h; /* row 2 */
position = position + 054h; /* row 3 */
end;
DO WHILE lcdbusy; /* wait till LCD ready */
END;
lcdregs = position + 080h;
END lcdscp;
END lcdscp;
- Writes a character to the LCD at the current cursor position.
- Function parameter:
character : character to be written
Code:
lcdwc:DO;
DECLARE lcddata BYTE EXTERNAL AUXILIARY;
lcdbusy:PROCEDURE BIT EXTERNAL;
END lcdbusy;
lcdwc:PROCEDURE(character) PUBLIC;
DECLARE character BYTE;
DO WHILE lcdbusy; /* wait till LCD ready */
END;
lcddata = character; /* write char. to LCD */
END lcdwc;
END lcdwc;
- Writes a string from auxiliary data memory (ext. RAM) to the LCD
starting at the current cursor position.
- Function parameter:
stringaddress : start address of the string in auxiliary data memory
length : length of the string
- 'length' = 0 : a $-terminated string is expected
- 'length' <> 0 : 'length' characters are written
Code:
lcdwsa:DO;
lcdwc:PROCEDURE(character) EXTERNAL;
DECLARE character BYTE;
END lcdwc;
lcdwsa:PROCEDURE(stringaddress,length) PUBLIC;
DECLARE stringaddress ADDRESS;
DECLARE character BASED stringaddress BYTE AUXILIARY;
DECLARE length BYTE;
DECLARE terminator LITERALLY '036'; /* ASCII code for '$' */
IF length = 0
THEN /* terminated string */
DO WHILE character <> terminator; /* while not end of string */
CALL lcdwc(character); /* write character */
stringaddress = stringaddress + 1; /* adress of next char. */
END;
ELSE /* string length specified */
DO WHILE length > 0; /* while not end of string */
CALL lcdwc(character); /* write character */
stringaddress = stringaddress + 1; /* adress of next char. */
length = length - 1; /* decrement length counter */
END;
END lcdwsa;
END lcdwsa;
- A 8031 (or derivate) is used to control the LCD.
- Needs decoded LCD-READ en LCD-WRITE signals, derived from controller signals AD00..AD07, A08..A15, /RD and /WR, to map the LCD into the external DATA area.
- Address line A00 is connected to the DEMULTIPLEXED controller signal AD00 and controls which LCD register is accessed.
- Data lines AD00..AD07 are directly connected to controller signals AD00..AD07.
- Control line 'BACKLIGHT' is used to switch the LED-backlight on (logic 1) or off (logic 0) or could be controlled from a PWM output.
An address decoder example for the schematic in 3.4.2.1.
is available as 2 seperate GIF files:
1. The 8031 uC part with address demultiplexer which generates the A00 signal.
View this gif.
2. The address decoder part which generates LCD-READ and LCD-WRITE signals.
View this gif.
