Endianness and shift operator in C language, am I doing it correctly?

Question

The original code works fine, it is :

for(i = 0; i < 8; i++){
  while(readPortAPin1() == BAIXO);
  writePortAPin2(value & 0x01);
  value >>= 1;
  while(readPortAPin1() == ALTO);
}

In the first code, if value = 10101010 it will be sent as 01010101. I would like to change the order of transmission, for example, if value = 10101010, I woul like to transmit 10101010.

To implement this, I did the following code:

for(i = 0; i < 8; i++){
  while(readPortAPin1() == BAIXO);
  writePortAPin2(value & 0x80);
  value <<= 1;
  while(readPortAPin1() == ALTO);
}

But, it is not working, it is transmiting all 0s. Am I doing something wrong ?

if `value` is b10101010 and you want to send b10101010, you don't need to change it. — dbush, Dec 13 '18 at 20:46
This has nothing to do with endianness. How is `value` declared? — n. m. could be an AI, Dec 13 '18 at 20:50
I suspect that yoy need to write to the bottom bit of the port so try replacing `writePortAPin2(value & 0x80);` with `writePortAPin2((value & 0x80) >> 7);` — Dipstick, Dec 13 '18 at 20:52
@Dipstick, maybe you are correct. I'll try as soon as I can, I'll post the result later — Daniel, Dec 13 '18 at 21:00
@Dipstick, I really need to write to the bottom bit of the port. When I did, it worked fine — Daniel, Dec 14 '18 at 11:43

n. m. could be an AI · Accepted Answer · 2018-12-14T09:53:59.940

1

Apparently writePortAPin2() writes the least significant bit of the operand. You need to write the most significant bit of value

Change this

writePortAPin2(value & 0x80);

to this

writePortAPin2((value >> 7) & 0x01);

edited Dec 14 '18 at 09:53

answered Dec 13 '18 at 20:57

n. m. could be an AI

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Endianness and shift operator in C language, am I doing it correctly?

1 Answers1