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2's Complement Bit toggle
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Guest
PostPosted: Sun Mar 08, 2009 1:37 pm     Reply with quote
Thanks again! I'm gonna connect the circuit this week and test your answers out. I will post again then. Very Happy
Guest
PostPosted: Fri Mar 13, 2009 10:57 am     Reply with quote
Ttelmah I finally had time to try out you code and it worked nicely.
Code:
int16 val_from_unit;
signed int16 numeric_val;

numeric_val=val_from_unit & 0x1FFF; //get the thirteen numeric bits
if (val_from_unit & 0x2000) numeric_val |= 0xE000; //sign extend

Very Happy Very Happy

One last question could you explain your second line of code? I'm not understanding what it is saying. Thanks again.
FvM



Joined: 27 Aug 2008
Posts: 2337
Location: Germany

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PostPosted: Fri Mar 13, 2009 1:18 pm     Reply with quote
Without sign extension you won't get any negative number, e.g. 0x2000 is understood as 8192, but it means -8192.
Sydney



Joined: 13 Feb 2009
Posts: 71

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PostPosted: Fri Mar 13, 2009 3:00 pm     Reply with quote
Its because your 14 bit number say 0b11111111111111 = -1 when its put into your 16 bit var it becomes 0b0011111111111111 = 16383, so the sign bit 14 needs copying into 15 and 16 to make it -1 again
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