How to 'flip' a port?

Projects Programming
1

Hello,

I am trying to connect a 1284P to a T6963C display using this library: http://code.google.com/p/arduino-t6963c/; I have made changes to the header files so that all the pins pf PORTA drive the data bus and four pins on PORTC - PC2, PC3, PC4 and PC5 drive the control pins.

Here is the edit:

#if (defined(__AVR_ATmega1280__) || \
     defined(__AVR_ATmega1281__) || \
     defined(__AVR_ATmega2560__) || \
     defined(__AVR_ATmega2561__))      //--- Arduino Mega ---

// data port Arduino Mega
#define GLCD_DATA_PORT	 	PORTL
#define GLCD_DATA_PIN		PINL		//Arduino Mega Pins 49-42
#define GLCD_DATA_DDR		DDRL

// control port Arduino Mega
#define GLCD_CTRL_PORT		PORTC
#define GLCD_CTRL_PIN		PINC		//Arduino Mega Pins 37-34
#define GLCD_CTRL_DDR		DDRC

#elif defined(__AVR_ATmega1284P__)

// data port 1284P
#define GLCD_DATA_PORT 		PORTA
#define GLCD_DATA_PIN		PINA	//Arduino Pins 2-7
#define GLCD_DATA_DDR		DDRA
#define GLCD_DATA_MASK		0xFF

// control port 1284P
#define GLCD_CTRL_PORT		PORTC
#define GLCD_CTRL_PIN		PINC
#define GLCD_CTRL_DDR		DDRC

// control signals 1284P
#define GLCD_WR 	2
#define GLCD_RD			3
#define GLCD_CE			4  //Should be able to XNOR this with WR and RD
#define GLCD_CD			5
//#define GLCD_RESET  		4  //For some reason my LCD works with this pin resistored to +5
//#define GLCD_FS     		5  //Use hardware solution not pin.

#else// data port other Arduino
#define GLCD_DATA_PORT1 	PORTD
#define GLCD_DATA_PIN1		PIND	//Arduino Pins 2-7
#define GLCD_DATA_DDR1		DDRD
#define GLCD_DATA_SHIFT1	<<2
#define GLCD_DATA_RSHIFT1	>>2
#define GLCD_DATA_MASK1		0xFC

#define GLCD_DATA_PORT2 	PORTB
#define GLCD_DATA_PIN2		PINB	//Arduino Pins 8,9
#define GLCD_DATA_DDR2		DDRB
#define GLCD_DATA_SHIFT2	>>6
#define GLCD_DATA_RSHIFT2	<<6
#define GLCD_DATA_MASK2		0x03
// control port
#define GLCD_CTRL_PORT		PORTC
#define GLCD_CTRL_PIN		PINC
#define GLCD_CTRL_DDR		DDRC

// control signals
#define GLCD_WR 		0
#define GLCD_RD			1
#define GLCD_CE			2  //Should be able to XNOR this with WR and RD
#define GLCD_CD			3
//#define GLCD_RESET  		4  //For some reason my LCD works with this pin resistored to +5
//#define GLCD_FS     		5  //Use hardware solution not pin.
# endif

What this has done is that PortA.0 goes to DB0, PortA.1 goes to DB1 etc., till PortA.7 to DB7.

In a gross oversight on my part, I designed and fabricated a few PCBs with the inverted connection - i. e., PortA.0 to DB7, PortA.1 to DB6 etc., till PortA.7 to DB0.

Now, to my question: is there a way , for lack of a better word, 'to flip' PortA in code so as to have proper transmission of data?

I am sorry if I have not used the proper terminology.

Thanks,
Madhu.

2

You mean this:

?

A better tutorial is here. http://www.avrfreaks.net/index.php?name=pnphpbb2&file=viewtopic&t=37871 further down there are a couple of Macros for bit manipulation.

3

Hello,

Thanks for replying. I realise that there is bit manipulation involved; but I am unsure how to do it.

What I am trying to achieve is to 'turn the port over on its head'.

Let me explain - The library is configured to use PortA.0 for DB0 and my PCB has PortA.7 for DB0. I need guidance with the bit where we change the order.

Thanks,
Madhu.

4

Like:
ABCDEFGH
to
HGFEDCBA
?

5

WizenedEE,

Exactly.

Thanks,
Madhu.

6

Say you want to access bit BIT, if you use the bit manipulation with (7-BIT) instead of BIT, you should achieve that.

7

Bubulindo,

I am sorry, I do not follow.

Do you want to see how the data port is being used by the library?

Thanks,
Madhu.

8

Do you have 256 bytes of flash (program) memory spare? You could do a table lookup.

9 
byte flip (byte a)
  {
  byte b;
  for (byte i = 0; i < 8; i++)
    {
    b <<= 1;
    if (a & 1)
      b |= 1;
    a >>= 1;
    }  
  return b;
  }  // end of flip

void setup () 
{
  Serial.begin (115200);
  Serial.println ("Start");
  Serial.println (flip (0x01), BIN);
  Serial.println (flip (0x02), BIN);
  Serial.println (flip (0x03), BIN);
  Serial.println (flip (0x40), BIN);
  Serial.println (flip (0xFF), BIN);
  Serial.println (flip (0xAE), BIN);
}

void loop () {}

Output:

Start
10000000
1000000
11000000
10
11111111
1110101
10

Mr. Gammon,

Has anyone told you lately that you are a godsend? Well, if not, please let me.

Your flip function performed flawlessly! Thank you ever so much!

Regards,
Madhu.