Hi Craig + Andy,

I am using assembly.

No I am not using the UART.

Actually the data is coming off an encoder which encodes with pulse width modulation.

In the idle state the pulse is constantly low so as the pulse goes high the input port the software starts measuring the pulse widths according to the data sheet of the encoder chip.

The difference between good and bad data is exactly the same way as you mentioned that the received byte is different from the expected byte.

The expected byte is read from the look up table.

Hey, its the first time I am effectively using lookup table in my code. Can it be a reason that the address offset is tooooo big that it never returns.

I don't think it can happen cuz, whether data bad or good the address offset is always constant and stored in a register and used by (mov a @a+pc).......

Simon