Is PSoC4's UART based on CMOS? I can't find the answer of this question in the datasheet of UART SCB Component.
It is of no relevance which technology the UART in the PSoC is "based" on, the communication with the outer world will be made through the GPIOs which are configurable for CMOS input levels. Have a look at the electrical characteristics of the pin component.
You need a chip similar to a MAX232. This chip converts your digital signal to RS232 levels. It generates the higher level from charge pump o. The chip. Failure to use a chip like this will destroy your Psoc 4 chip.
Oh, yes! Bob is right ;-) When using an RS232 device you always will need a signal level converter connected to your UART.