Atmel C code understanding

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aliyesami

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this is a working code that is combining the databits on two different ports and I am not understanding how it is working.
if we AND PORTB to ~0x3F which is 0xC0 , it will make bits DB0-DB5 all zeros so how is the PORTB and PORTC
assignments working ?

Code: 
/*-------------------------------------------------
DATA mapping:
    DB0    DB1   DB2    DB3   DB4   DB5    DB6   DB7 
    
    PB0    PB1   PB2     PB3   PB4   PB5    PC6   PC7

CONTROL mapping:
    RES  RD   WR  RS
    PC2  PC3  PB4 PB5
    
---------------------------------------------------*/
 #define DMSK				0x3F
 

void write_8(unsigned char c)
{
	PORTB = (PORTB & ~DMSK)|(c & DMSK); 
	PORTC = (PORTC & DMSK)|(c & ~DMSK);
     	.
	.
}

void TFT_setup(void)
{
	DDRB |= DMSK;               
	DDRC |= ~DMSK;			
	DDRC |= 0x3C;              
        .
        .
}
 

At the top you have the pinout guide showing what maps to what. From the look of it is to a LCD. DB0 connects to PORTB.0, DB1 connects to PORTB.1 and so on

Next is a constant declaration. 0x3F hex is for 00111111. This is later on in the code

The first line in write_8 places lower 6 bits of input c on the lower 6 bits of PORTB or DB0-DB5.
The next line places the upper 2 bits of input c on the upper 2 bits of PORTC or DB6-DB7.

The first line in TFT_setup sets the lower 6 bits of DDRB to 1.
The next line sets the upper 2 bits of DDRC to 1.
The next line sets the middle 4 bits of DDRC to 1.

This code used bit wise operations to set and clear the data lines for PORTB and PORTC.
 

so i change the pin mapping to

DATA:
DB0 DB1 DB2 DB3 DB4 DB5 DB6 DB7

PB0 PB1 PB2 PC3 PC4 PC5 PC6 PC7

CONTROL:
RES RD WR RS
PC2 PB5 PD3 PD2
Click to expand...

would the following code works ?

Code: 
void write_8(unsigned char c)
{
 	PORTB = (PORTB & 0xF8)|(c & 07);  // Read PORTB and mask to keep upper 5 bits, Mask c to keep lower 3 bits,  OR both together and write back to PORTB
 	PORTC = (PORTC & 1F)|(c & F8);    // Read PORTC and mask to keep lower 3 bits, mask c to keep upper 5 bits,  OR both and write back to PORTC
}

void TFT_setup(void)
{
DDRB |= ((1<<PORTB0)|(1<<PORTB1)|(1<<PORTB2)|(1<<PORTB5)) 
DDRC |= ((1<<PORTC2)|(1<<PORTC3)|(1<<PORTC4)|(1<<PORTC5)|(1<<PORTC6)|(1<<PORTC7))
DDRD |= ((1<<PORTD2)|(1<<PORTD3))
}

please note I am using one DDRC command to set the data and control bits as output and not two DDRC commands as in original post.
 
Last edited:

Code: 
PORTC = (PORTC & 1F)|(c & F8);    // Read PORTC and mask to keep lower 3 bits, mask c to keep upper 5 bits,  OR both and write back to PORTC
This should be:
PORTC = (PORTC & 0x07) | (c & 0xF8);

Code: 
DDRB |= ((1<<PORTB0)|(1<<PORTB1)|(1<<PORTB2)|(1<<PORTB5)) 
DDRC |= ((1<<PORTC2)|(1<<PORTC3)|(1<<PORTC4)|(1<<PORTC5)|(1<<PORTC6)|(1<<PORTC7))
DDRD |= ((1<<PORTD2)|(1<<PORTD3))
This should be:
DDRB |= 0x27;
DDRC |= 0xFC;
DDRD |= 0x0C;
 

bluelasers said:
Code: 
PORTC = (PORTC & 1F)|(c & F8);    // Read PORTC and mask to keep lower 3 bits, mask c to keep upper 5 bits,  OR both and write back to PORTC
This should be:
PORTC = (PORTC & 0x07) | (c & 0xF8);
Click to expand...

oops yes i see my mistake .. thanks

I am not understanding why? what am I doing wrong in setting all the output pins direction to 1 ?

thanks
 


I think the macros are PB0 style instead of PORTB0 style. I could be wrong. Either way you could just manually encode them in hex. Which is shorter.
 
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