I've found out another couple of problems in using ATMEL AT89S8253 that I'd like to share with the forum.

Slobodan Mandaric already told us of the problem with the ISP positive/negative edge of the clock in another thread (by the way, thank you Slobodan).

Now I've found (upgrading from AT89S53):
1) The XTAL clock OUTPUT is at a very low level (about 1V), and it can not drive a clock INPUT of another microcontroller, such as a small P87LPC764 that I used as bootloader with the previous AT89S53. Atmel told me to try 10pF capacitors on the crystal, or no caps at all, but it does not work. I will have to change the PCB adding another crystal for the P87LPC764.

2) The flag TF2 (Timer 2 interrupt flag) can not be set by software. Or better to say: it can be set by software, but it will not generate any interrupt.
Workaround: if you want to generate a software interrupt you can use EXF2.


Regards,

Fausto Marzoli