SCADA-CPU Communication

I have machine with two different CPU for different function provided by different client. CPU 319-3PN/DP is installed with 4 profibus dp node and one scada station. CPU 315-2DP is used with one node for profibus encoder.

Now i use only one cpu 315-2dp and make cpu 319 as spare. so installed modified the hardware and club the logic. logic is working ok. installed cpu 315 in place of cpu319 and installed IM153-1 in placed of CPU 315.

Now scada station communication time out again and again means all the input and output filed area are blink out. But same time if i used CPU319 in place of CPU315 by modified the hardware, No communication problem found. SCADA Station is available with profibus card installed in PCI slot.

so first i have updated the firmware of CPU315-2DP. After that that communication failure decrease it is now around 1 hour 1 time failure and within few second again ok and during failure all the input output area data is hide.

So please suggest me why this happen because whole system with CPU319 working ok but with CPU315 this communication on/off on scada occure.

wait for positive reply.

Thanks and regards,
Kalpesh Makvana