Hi Fran,

The /INT0 pin act also as gate for T0 (/INT1 for T1).
If the Gate bit on TMOD is set, CT0 can only count
during high on /INT0.
Also you must set TL0 and TH0 to 0FFh.

Then every time if /INT0 goes high T0 roll over and
generate a T0 interrupt on the next cycle.

The T0 interrupt handler should disable itself (clr ET0)
and enable /INT0 (setb EX0).
Then the /INT0 interrupt can serve the low state
and reenable T0 (also must set TL0 and Th0 to 0FFh again).

If you set T0 to the 8-bit auto reload mode you must only
after reset load TL0 and TH0 with 0FFh, not during every
/INT0 interrupt.

If you need T1 for the UART and also a timer interrupt,
you can split T0 in 2 timers: TL0 to serve high on /INT0
and TH0 as 8 bit timer.
Then TH0 use interrupt T1, but this is no problem, since
T1 need its interrupt no longer, if acting as
baud rate genrator for the UART.


Regards,
Peter