Zinc-7000 returns unread bytes of information to UART

Question

I have a ZC702 Evaluation Kit with a Zynq-7000 processor. I need to transfer the array of information from the PC to the board via the "USB UART" connector, process it, and give a response to the PC. The ZC702 Evaluation Kit is loaded from the SD card on which PetaLinux is installed. To convert USB-UART on the board is used CP2103 Silicon Lab. Why, when reading data on the board (for example, with the command "cat /dev/ttyPS0"), the zero byte does not return once. At the same time, he will be sent back to the PC. If the board does not start reading from /dev/ttyPS0, the entire array of data will be returned to the PC.