+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,
+ # with bit numbers changed 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.implied_newline = False
+ 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: # Lines 2 & 3 add number of columns
+ addr += self.num_columns
+ 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':
+ if self.implied_newline:
+ # self.implied_newline means we advanced due to a wraparound,
+ # so if we get a newline right after that we ignore it.
+ pass
+ else:
+ self.cursor_x = self.num_columns
+ else:
+ self.hal_write_data(ord(char))
+ self.cursor_x += 1
+ if self.cursor_x >= self.num_columns:
+ self.cursor_x = 0
+ self.cursor_y += 1
+ self.implied_newline = (char != '\n')
+ 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))
+ self.hal_sleep_us(40)
+ for i in range(8):
+ self.hal_write_data(charmap[i])
+ self.hal_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
+
+ def hal_sleep_us(self, usecs):
+ # Sleep for some time (given in microseconds)
+ time.sleep_us(usecs)
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