This page is intended to show the outline of the chip and to provide additional information that might not be clear from the data sheet.
The tiny4313 has an internal oscillator that can run at various frequencies. The 4 MHz seems not to work precise. when using the UART for serial communication you can get wrong output. You can best use the 8 MHz internal oscillator , or tweak the UBRR register. For example, UBRR=UBRR+1
That worked for 4 Mhz, at 19200 baud.