suppose while DATA0=0 main program is carrying out other code.till the other code is complete,DATA0 has became 1.so a 0-bit has been lost.
the even-odd check of the cardno must haven't been passed,and it seems MCU can't receive cardno from ID modual.the only method is receive every bit in the extral interrupt routine.
(it isn't correct only make a flag 1 to indicate the start receiving of the cardno.because the main routine is carrying out other code and not reach the code where the flag is enqiried although the flag is 1)