"result on serial port (PC hyperterminal)
"test = -221846,0" STRING visible.

I presume that 1st number should be -21846?

I also presume that you must have disabled the ANSI integer promotions?

Now, let's consider your format string:
"test = %d,%dn"
The two %d specifiers tell sprintf to expect two int values; ie, two 16-bit values;
Without the ANSI integer promotions, your two values - 170 (=0xAA) and 0xAA - are both single bytes.

Therefore, when you run this, the 1st %d looks for its 16-bit value and takes both of your bytes at once to make 0xAAAA = -21846.
The behaviour of the 2nd %d - as you haven't supplied enough actual parameters - is undefined!

You need to be very careful that the actual parameters precisely match the format specifiers!

You must either change your specifiers, or cast your bytes to ints!