Forum Post: RE: Why a opcode can't using in CCS 3.3

another question, can you help me ?

i want to finish a multiply:  -32768 x 32768.

so the code is follwing: 

mpy in1,in2,result
stnw in1,*out1++
stnw in2,*out1++   
stnw result,*out1++

I printf them :  printf("%x\n",out1[i]);

FFFF8000
8000
40000000

you know that is worng! why ?  

is that mpy can finish this task :Multiply Signed by Signed, 16 LSB × 16 LSB