Atmel M90E26 energy meter
Once you make an energy meter, it won't directly give you the accurate reading of 3200 impulses per kWh. You need to calibrate each energy meter circuits individually against a standard meter.

For your chip (M90E26), it requires writing to some calibration registers. Check section 3 of your document.

If this calibration process looks too complicated to you, you can go for simpler chips where calibration requires shorting of binary ladder resistors on the voltage sampling channel. Example of such an IC - BL0921.