Hi samynonsense,

1.
Only timer 1 can be used to generate the baud rate. But no timer interrupt was used, the timer 1 overflow was feed direct into the UART hardware. Please refer on the data sheet about the built-in UART.

2.
Using printf() inside the interrupt can cause many trouble and eating many execution time. Thus it was possible, that some interrupts are lost. Better you store the value inside the interrupt and send this value inside the main().

3.
There are 2 interrupt priorities on the 8051 family. Some other derivates support also up to 4 different priorities.
The priority can be determined separate for every interrupt source. Please refer on the data sheet about the IP register.



Peter


P.S.:
Seems, you should consider a more serious nickname.