This is part of the code, it write to LCD.
Hitachi HD44780. It uses it in 4 bit mode
PORTB bits 0-3 are connected to the LCD data bits 4-7 (high nibble)
Code:lcd_putch(char c) { LCD_RS = 1; // write characters PORTB = (PORTB & 0xF0) | (c >> 4); LCD_STROBE; PORTB = (PORTB & 0xF0) | (c & 0x0F); LCD_STROBE; DelayUs(40); }
I cannot understand the next rows:
PORTB = (PORTB & 0xF0) | (c >> 4);
PORTB = (PORTB & 0xF0) | (c & 0x0F);
What about them can't you understand?
> PORTB & 0xF0
Preserves the top 4 bits, and clears the bottom 4 bits.
The two operations on c get the top 4 bits and bottom 4 bits into position read to add (using |) to the existing portb value.
If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
If at first you don't succeed, try writing your phone number on the exam paper.
What role is this expression do: (c >> 4)
Easily answered by looking in a book.
If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
If at first you don't succeed, try writing your phone number on the exam paper.
It shifts the bits in c to the right by 4 places.
So if c looked like:
10100000
It would now look like:
00001010
and c better be unsigned char for thisOriginally Posted by DavidP
All problems in computer science can be solved by another level of indirection,
except for the problem of too many layers of indirection.
– David J. Wheeler
