Wierd Mega1280 fault

Other Hardware 3rd Party Boards
1

Has anyone come across this one before:

If I write something to D33, it appears on both D33 and D34. If I write to D34, nothing happens.

I have checked with a multimeter and the pins aren't shorted out, and D33 connects to pin57, while D34 connects to pin58 as I would expect.
And yet... ?

Here is the test code I used:

int led = 33;
int led2 = 34;

void setup() {                
  pinMode(led, OUTPUT);     
  pinMode(led2, OUTPUT);     
}

void loop() {
  digitalWrite(led, HIGH);  
  digitalWrite(led2, HIGH);  
  delayMicroseconds(100);    
  digitalWrite(led, LOW);    
  delayMicroseconds(100);               
  digitalWrite(led, HIGH);   
  digitalWrite(led2, LOW);    
  delayMicroseconds(100);               
  digitalWrite(led, LOW);    
  delayMicroseconds(100);              
}

Basically 33 and 34 should oscillate at at different rates, but when viewed on a logic analyser they both oscillate at the same rate.
If I change:
led2=34
to:
led2=35

then 33 and 34 oscillate at the same rate, whilst 35 oscillates at half the rate.

If I then change it to be:
led = 34
led2 = 35,

then neither 33 nor 34 oscillate, but 35 oscillates at the rate it did before.

Any ideas? Or is my atmega1280 chip broken.

2

Which version of the IDE are you using? On my Mega2560 it appears to work correctly, the way you describe it should.

3

Can you do a verbose output, find the .elf file, and then do this ...

avr-objdump -S xxxx.elf > myoutput.txt

Then post the output file here as an attachment.

4

Its the latest IDE (1.0.1), with an Arduino Mega 1280.

I have attached the assembler.

I have had a look at the pins_arduino.h file and it appears in order.

assembler.txt (30.6 KB)

5

Can you run this sketch please and post what you get:

int led = 33;
int led2 = 34;

void setup()
{                
  Serial.begin (115200);
    
  Serial.println ("led");
  Serial.println (digitalPinToPort (led), HEX);
  Serial.println (digitalPinToBitMask (led), HEX);
  Serial.println (digitalPinToTimer (led), HEX);
  Serial.println ((int) portOutputRegister (digitalPinToPort (led)), HEX);
  
  Serial.println ("led2");
  Serial.println (digitalPinToPort (led2), HEX);
  Serial.println (digitalPinToBitMask (led2), HEX);
  Serial.println (digitalPinToTimer (led2), HEX);
  Serial.println ((int) portOutputRegister (digitalPinToPort (led2)), HEX);   
}

void loop() { }

I got:

led
3
10
0
28
led2
3
8
0
28
6 
led
3
10
0
28
led2
3
8
0
28

Just as with yours.

7

Sounds like you might have a dodgy chip.

8

Yeah, thats what I was thinking. I will have to get a new atmega1280 chip and attempt to replace the chip. Actually I might get a 2560 as they are pin compatible, I might aswell get more flash space while I'm at it!

9

On second thoughts, i'll just get a new board. Its going to be too much of a pain trying to solder with the connectors in the way. Plus apart from that 1 pin, the board works fine. So if I get a whole new one, I'll have two :smiley: I think I might put a bit of super glue down the hole for D34 so I know not to use it...