There are basicly three methods:

1.
You have some distinct char/pattern in the stream that signals end-of-data.

2.
You have a timeout (no data on the line) that singnals end-of-data.

3.
Your data has always a fixed lenght.

Pick what works for you.

The timeout counter should be reset/zeroed in the UART-ISR and
the "counting" should be done elsewhere (in main or in another
timer-ISR).

Jan-Erik.



Andre Abelian wrote 2014-02-02 18:50:
> Hi All,
>
> I am having hard time to determine the length of  uart RX data. the data =
length is unknown it is between (100-125 byte) and it is less then 128 byte=
s.
> in my routine RX ISR clears the RX flag and saves the byte came in and in=
creases the counter. data_available is not used for now
>
> void __attribute__((interrupt, no_auto_psv)) _U2RXInterrupt(void) {
>
>      uint8_t data_size_U2;
>
>          IFS1bits.U2RXIF =3D 0;
>          if (U2STAbits.URXDA =3D=3D 1)
>          {
>              U2_RX[new_counter] =3D U2RXREG;      // save incoming byte
>
>              counter++;     // increment
>              data_available =3D 1;
>              GLED_ON;
>          }
>
> }
>
>
> the counter contains total number of bytes but the question is how to che=
ck when no more data is coming in? to use the counter.
> I was testing with IDEL flag     U2STAbits.RIDLE I can see when uart RX i=
s active  the flag is set to 0. now the problem is
> even on first receive byte the flag will indicate as busy. so just using =
when it is busy is not going to work.
> in my case I do not mind to deal with fixed 128 byte every time I already=
 know the data is some where between
> 100-125 bytes. the only issue is when there is no data coming in the inte=
rrupt will not occur and counting extra is not going to work.
>   the counter in ISR knows exact  length of bytes came in but I do not kn=
ow when to check the counter since I do not know the length of data.
> i am not sure if I explain clearly. the counter and U2_RX are global vari=
ables.
>
> any idea or suggestion will appreciate.
>
> thanks
>
> Andre
>
--=20
http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist
.