display-library

Small, fast library written in AVR assembler.

Can be used with standard C/C++ compilers, ARDUINO or pure assembler programming

• for HD44780 compatible LCD's, support for
  • 8/4 bit interface
  • 3 wire serial interface based on 74HCT164
• for LED MAX7221 driver (not yet implemented)

Mandatory settings

The following bit constants must be set in the source-file:

4 / 8 bit mode

• _RS Register Select (shared with serial data in 3 wire mode)
• _RW Read-write (not needed in 3 wire mode)
• _EN Enable

3 wire interface

• _SD Serial data (shared with register select)
• _SC Serial clock

Example:

; define control bits
.equ _RS, 3     ; register select: data=1, control=0
.equ _RW, 5     ; read/write: read=1, write=0
.equ _EN, 4     ; enable: active high

; for 3-wire interface (using 8-bit shift register 74xx164)
.equ _SD, _RS   ; serial data (shared with lcd register select)
.equ _SC, _RW   ; serial clock (RW not needed in serial mode)

Functions HD44780

initLCD(void)

This function initializes the display. You can choose the mode in the source-file (hd44780.S) by commenting out the required assembler definitions:

;.set __4BIT__, true             ; if set the 4-bit interface of the display will be used
;.set __USE_4TO7__, true         ; if set the upper 4 bits (4-7) of the specified port will be used
;.set __3WIRE__, true            ; if set the 3-wire interface (74xx164) will be used

libinfo(void)

An info about the library version and mode will be displayed.

writeLCD(char rs, char data)

The writeLCD function send the data to the selected register rs=0 => control or rs=1 => data

char readLCD(char rs)

Reads the data from selected register rs=0 => control or rs=1 => data

printxyLCD(char x, char y, const char *text)

The given text is display at column x and row y. The numbering starts at '1'.

printLCD(const char *text)

Same as above, but prints at current cursor position.

newCHR(char addr, const char *character)

Creates an new character in CGRAM. You can define 8 independent characters, the numbering starts at addr '0'. The function expects an array for *character in the following format:

.byte 0x0e, 0x1f, 0x11, 0x11, 0x11, 0x11, 0x11, 0x1f

char data[] = {0x0e, 0x1f, 0x11, 0x11, 0x11, 0x11, 0x11, 0x1f};

The example shows a battery 😉.

mswait(int ms)

This functions waits for ms milliseconds.

You can adapt the settings in include/delay.asm, to find the best values DelayCalc.ods can help you. Simply enter the CPU frequency and the desired delay, the best correction factor can then be found out by trial and error. Hint: Look at the field with the deviation.

Note: The sheet is locked, values can only be entered in the green fields.

uswait(int us)

Same as above but waits for us microseconds.

This function works only with 6, 12, 16 and 20 MHz correct.

wait (local hd44780.S)

Internal wait for some display functions.