How Siemens S7-200 series PLC’s power requirements and calculation?

S7-200 CPU module provides 5VDC and 24VDC power supply:
When an expansion module CPU through I / O bus to provide 5V power supply, all the expansion module 5V power consumption of the CPU and can not exceed the rated power provided. If not enough external 5V power supply. Each CPU has a 24VDC sensor power supply, it is native input and expansion module input and expansion modules provide relay coil 24VDC.
If the power requirement exceeds the power budget of the CPU module, you can add an external 24VDC power supply to provide to the expansion module.
The so-called power calculation is to use the CPU can provide power capacity, minus the modules required to power consumption.
Note: EM277 module itself does not require 24VDC power supply, the power supply is designed for communication port used. 24VDC power supply requirements depend on the size of the load on the communication ports.
Communication port on the CPU, you can connect PC / PPI cable and TD 200 and give them power, the power consumption has no longer included in the calculation.