Dear Hari,
As Dora rightly pointed out you may use the operation CMPER to compare two period specifications in three different variants. The periods used in the comparison are the in-period and for-period of the current payroll run.
You will get more details on the payroll operation from SAP help documentation.
Below is an illustrative example -
.As shown in the CMPER 1301 operation the for-period is compared with period 01 of year 2013 and based on the for-period either "*" or "<" is placed in the variable key which further takes the control of the PCR.
Hope this helps.
Regards,
Arnab