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"""Provides an API for talking to HD44780 compatible character LCDs."""
import time
class LcdApi:
"""Implements the API for talking with HD44780 compatible character LCDs.
This class only knows what commands to send to the LCD, and not how to get
them to the LCD.
It is expected that a derived class will implement the hal_xxx functions.
"""
# The following constant names were lifted from the avrlib lcd.h
# header file, however, I changed the definitions from bit numbers
# to bit masks.
#
# HD44780 LCD controller command set
LCD_CLR = 0x01 # DB0: clear display
LCD_HOME = 0x02 # DB1: return to home position
LCD_ENTRY_MODE = 0x04 # DB2: set entry mode
LCD_ENTRY_INC = 0x02 # --DB1: increment
LCD_ENTRY_SHIFT = 0x01 # --DB0: shift
LCD_ON_CTRL = 0x08 # DB3: turn lcd/cursor on
LCD_ON_DISPLAY = 0x04 # --DB2: turn display on
LCD_ON_CURSOR = 0x02 # --DB1: turn cursor on
LCD_ON_BLINK = 0x01 # --DB0: blinking cursor
LCD_MOVE = 0x10 # DB4: move cursor/display
LCD_MOVE_DISP = 0x08 # --DB3: move display (0-> move cursor)
LCD_MOVE_RIGHT = 0x04 # --DB2: move right (0-> left)
LCD_FUNCTION = 0x20 # DB5: function set
LCD_FUNCTION_8BIT = 0x10 # --DB4: set 8BIT mode (0->4BIT mode)
LCD_FUNCTION_2LINES = 0x08 # --DB3: two lines (0->one line)
LCD_FUNCTION_10DOTS = 0x04 # --DB2: 5x10 font (0->5x7 font)
LCD_FUNCTION_RESET = 0x30 # See "Initializing by Instruction" section
LCD_CGRAM = 0x40 # DB6: set CG RAM address
LCD_DDRAM = 0x80 # DB7: set DD RAM address
LCD_RS_CMD = 0
LCD_RS_DATA = 1
LCD_RW_WRITE = 0
LCD_RW_READ = 1
def __init__(self, num_lines, num_columns):
self.num_lines = num_lines
if self.num_lines > 4:
self.num_lines = 4
self.num_columns = num_columns
if self.num_columns > 40:
self.num_columns = 40
self.cursor_x = 0
self.cursor_y = 0
self.backlight = True
self.display_off()
self.backlight_on()
self.clear()
self.hal_write_command(self.LCD_ENTRY_MODE | self.LCD_ENTRY_INC)
self.hide_cursor()
self.display_on()
def clear(self):
"""Clears the LCD display and moves the cursor to the top left
corner.
"""
self.hal_write_command(self.LCD_CLR)
self.hal_write_command(self.LCD_HOME)
self.cursor_x = 0
self.cursor_y = 0
def show_cursor(self):
"""Causes the cursor to be made visible."""
self.hal_write_command(self.LCD_ON_CTRL | self.LCD_ON_DISPLAY |
self.LCD_ON_CURSOR)
def hide_cursor(self):
"""Causes the cursor to be hidden."""
self.hal_write_command(self.LCD_ON_CTRL | self.LCD_ON_DISPLAY)
def blink_cursor_on(self):
"""Turns on the cursor, and makes it blink."""
self.hal_write_command(self.LCD_ON_CTRL | self.LCD_ON_DISPLAY |
self.LCD_ON_CURSOR | self.LCD_ON_BLINK)
def blink_cursor_off(self):
"""Turns on the cursor, and makes it no blink (i.e. be solid)."""
self.hal_write_command(self.LCD_ON_CTRL | self.LCD_ON_DISPLAY |
self.LCD_ON_CURSOR)
def display_on(self):
"""Turns on (i.e. unblanks) the LCD."""
self.hal_write_command(self.LCD_ON_CTRL | self.LCD_ON_DISPLAY)
def display_off(self):
"""Turns off (i.e. blanks) the LCD."""
self.hal_write_command(self.LCD_ON_CTRL)
def backlight_on(self):
"""Turns the backlight on.
This isn't really an LCD command, but some modules have backlight
controls, so this allows the hal to pass through the command.
"""
self.backlight = True
self.hal_backlight_on()
def backlight_off(self):
"""Turns the backlight off.
This isn't really an LCD command, but some modules have backlight
controls, so this allows the hal to pass through the command.
"""
self.backlight = False
self.hal_backlight_off()
def move_to(self, cursor_x, cursor_y):
"""Moves the cursor position to the indicated position. The cursor
position is zero based (i.e. cursor_x == 0 indicates first column).
"""
self.cursor_x = cursor_x
self.cursor_y = cursor_y
addr = cursor_x & 0x3f
if cursor_y & 1:
addr += 0x40 # Lines 1 & 3 add 0x40
if cursor_y & 2:
addr += 0x14 # Lines 2 & 3 add 0x14
self.hal_write_command(self.LCD_DDRAM | addr)
def putchar(self, char):
"""Writes the indicated character to the LCD at the current cursor
position, and advances the cursor by one position.
"""
if char != '\n':
self.hal_write_data(ord(char))
self.cursor_x += 1
if self.cursor_x >= self.num_columns or char == '\n':
self.cursor_x = 0
self.cursor_y += 1
if self.cursor_y >= self.num_lines:
self.cursor_y = 0
self.move_to(self.cursor_x, self.cursor_y)
def putstr(self, string):
"""Write the indicated string to the LCD at the current cursor
position and advances the cursor position appropriately.
"""
for char in string:
self.putchar(char)
def custom_char(self, location, charmap):
"""Write a character to one of the 8 CGRAM locations, available
as chr(0) through chr(7).
"""
location &= 0x7
self.hal_write_command(self.LCD_CGRAM | (location << 3))
time.sleep_us(40)
for i in range(8):
self.hal_write_data(charmap[i])
time.sleep_us(40)
self.move_to(self.cursor_x, self.cursor_y)
def hal_backlight_on(self):
"""Allows the hal layer to turn the backlight on.
If desired, a derived HAL class will implement this function.
"""
pass
def hal_backlight_off(self):
"""Allows the hal layer to turn the backlight off.
If desired, a derived HAL class will implement this function.
"""
pass
def hal_write_command(self, cmd):
"""Write a command to the LCD.
It is expected that a derived HAL class will implement this
function.
"""
raise NotImplementedError
def hal_write_data(self, data):
"""Write data to the LCD.
It is expected that a derived HAL class will implement this
function.
"""
raise NotImplementedError
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