HI Lobna,
this can be achieved multiple ways but here is one of the simplest way you would be able to achieve your requirements,
you would be to be hands on writing PCRs. below are the steps
1. maintain 3300 EGP as a constant in your payroll constants table. (your PCR will check value against this constant (this way it will be handy to change the value if the base ceiling value changes in future.
2. write a PCR to do a check against your basic salary ,if greater than 3300 deduct amount form 3300 and add that amount into a cumulation WT (say XY01 and store it in CRT to carry that value for the future use.
3. if the the base salary is less than 3300 write within your PCR to call the CRT value of XY01 and calculate difference to add into your base salary. rest of the value of XY01 should still cumulate for future use in CRT.
now couple of things to be considered here, CRT values are restored to zero at the end of the tax year so your will have to write another PCR to transfer the value of XY01 (cumulated value) into the first period of new tax year.
secondly you will also have to consider a scenario where employee might not have enough cumulated value of XY01 to be added into salary into a period where his/her salary is less than 3300.
hope this helps
KR
Sid