Accessing Bits

SRLM

Hi

How do you get into the individual bits of a long? I'm working through a protocol that needs a start bit of 0 and a stop bit of 1, along with a parity bit.

Also, is there an easy way to get a bit that tells the odd parity? I was going to use something like a loop and two counters, but I suspect that there must be an easier way.

Thank you.

Mike Green

To get individual bits you have to use various combinations of shifts and logical and/or/xor.

In assembly language, the logical operations put the parity of the result into the carry flag. In Spin there's no easy way. You can write an expression that xor's all the bits of interest together to get the parity. For serial communications, it's not too hard:

char |= (((char >> 6) ^ (char >> 5) ^ (char >> 4) ^ (char >> 3) ^ (char >> 2) ^ (char >> 1) ^ char) << 7) & %10000000

This converts a 7 bit value to 8 bits including odd parity.

nohab

Interesting row... gives "high level language" a new meaning

Can you give a short lesson how to read/interpret that, please ?!

SRLM

What about 8 bits into a one bit parity?

It looks like what you're doing is shifting bits right, then I get lost with the chevron and amperstand.

Any explanation would be great. Also, I took a more beginer's approach and wrote a good 'ole for-loop.

PUB getOddParity (Value) : bit | counter, index

  repeat index from 0 to 7
    'If the modulus of the number is even, then the last bit is a 0, if it's odd, then it's a 1
    if((value >> index) // 2 )
      'Must be a 1 bit at the end
      counter ++
    

  if(counter // 2)
    bit := 1
  else
    bit := 0

  if Value == 0
    bit := 1
      

Looks okay to me. Are there any errors that anybody can spot?