The UART0 is a debugging console. The logic level is 1.8V.
PlayStation TV UART0 location
OLED Vita UART0 location
Two ways of using UART0. First is to solder directly to the testpads near the PMIC (yellow and cyan points). The second way is through the multi-connector or the testpads above it (blue and red points). To use the multi-connector points though, you need either to tell the syscon to select the Kermit UART (procedure currently unknown) or manually flip the switch (green point to 1.8V).
OLED Vita UART5 location
It is on the PCI-E connector pins 8,10,12,14 is RFR, CTS, TX, RX. On Wifi Vita units, you need to fill in the 88ohm termination resistors (or just short the pads) and some way to enable it (not known yet).
ScePervasiveForDriver_EFD084D8(uart_bus); // Turn on clock ScePervasiveForDriver_A7CE7DCC(uart_bus); // Out of reset ksceUartInit(uart_bus); /* * Use UART bus * ... */ ScePervasiveForDriver_788B6C61(uart_bus); // Put to reset ScePervasiveForDriver_18DD8043(uart_bus); // Turn off clock