Hello,
Regarding all your ideas and things I would try, I'm trying to clean program by limiting the calls to my function which feed the watchdog.
I realize that the best code is to have only one call to this function in my main loop, but it's impossible.

About this, I have a question or a tip to ask to you :

I've got a serial port communication between my board (the micro) and any device (PC, modem or else).

currently I proceed as follow :

When I've to send data from micro :
- I feel a char* buffer (using sprintf)
- I enter a function (flush) which do this :
+ Activate serial interrupt (setting TI0=1)
+ enter an infinite loop while the number of chars to send isn't equal to 0
- In my serial interrupt I do if (TI0 == 1) :
+ SOBUF = char to send
+ feed watchdog (PCON=PCON|0x10; and T3=0x00;)
+ decrease number of chars to send
+ TI0 = 0

I would like to write a more suitable code for this algorithme.

The problem is that I can't send all the chars without feed the watchdog. baudrate can be between 300bds and 19200bds and the amount of data is about 250 chars at once and never excede a frame of 1000 chars (4 sprintf and 4 call to the flush function

In addition, I checked the init of the RAM at start (after a reset). Good news : the RAM isn't initialized, so I'm writing a code to set a variable in start of each function of my program which is displayed at start of the micro. So I'll can see in which function the program freezed.