Serial Syntax Question: What is this doing?

fmaurer

I don't understand what my code is doing; the result is unexpected in my eyes.

I'm reading serial bytes on my propeller using JDCogSerial (http://obex.parallax.com/objects/398/) and this command:

recByte = Comm.rxCheck
if (recByte <> -1)
      ... do something

If I send $FF, the firmware will run the code inside the "if" (but I don't want it to). I need it to only perform the code inside when a byte is received. I'm assuming that $FF can also be -1 and this is causing the problem?

Here's the rxCheck function definition:

PUB rxcheck : rxbyte
{ Check if byte received (never waits)
  returns < 0 if no byte received, $00..$FF if byte }
  if (rxbyte := rx1_buf) => 0
    rx1_buf := -1

Is there a way to check if a byte is received, and if so do something with it (even if it is 255)?

My code runs fine if I make sure I don't send a byte value of 255 (I cap everything at 254).

Sapieha

Hi fmauer.

"
if (recByte <> -1)" Is not $FF - But $FFFFFFFF.
And $FF are still received Character = 255 Decimal.

You need always check for -1 for no received character.

fmaurer wrote: »

I don't understand what my code is doing; the result is unexpected in my eyes.

I'm reading serial bytes on my propeller using JDCogSerial (http://obex.parallax.com/objects/398/) and this command:

recByte = Comm.rxCheck
if (recByte <> -1)
      ... do something

If I send $FF, the firmware will run the code inside the "if" (but I don't want it to). I need it to only perform the code inside when a byte is received. I'm assuming that $FF can also be -1 and this is causing the problem?

Here's the rxCheck function definition:

PUB rxcheck : rxbyte
{ Check if byte received (never waits)
  returns < 0 if no byte received, $00..$FF if byte }
  if (rxbyte := rx1_buf) => 0
    rx1_buf := -1

Is there a way to check if a byte is received, and if so do something with it (even if it is 255)?

My code runs fine if I make sure I don't send a byte value of 255 (I cap everything at 254).

Ps. That give You possibility to receive all characters from 0 to 255

Dave Hein

fmaurer,

Can you post all your code? rxCheck should be doing the right thing. Maybe there is a problem in how you handle recByte. If you happened to declare recByte as a byte or word it will never contain a value of -1, but will be 255 or 65535 instead.

A value of 255 is as valid as any other 8-bit value. It shouldn't cause your code to do anything differently unless you are testing for 255.

Dave