signed/unsigned multipliers

--- Quote Start ---

Hi tricky,

I am afraid they are not. not only MSB meaning is different, addition/subtraction are similar(taking into account carry bit difference).

multiplication/div are different.

--- Quote End ---

Yes they are.....

take the following example:

0111 x 1011

Lets assume it is unsigned (7 x 11). Add 0's forward

00000111 x 00001011

result =

 00000111
+    111
+                  
+  111
----------------
 01001101   (77)

Now do the same but assume its signed (7x-5)

sign extend both inputs to 8 bits

00000111 x 11111011

         00000111
       +     111
       +
       +   111
       +  111
       + 111
       .... etc
--------------------
= (..111)11011101 (= -35)

now if you had treated this as unsigned (251 x 7) the result would be

11011011101 (1757) see the resemblence yet?

--- Quote Start ---

I still don't understand why signa and signb aren't available though.

--- Quote End ---

That is because the LPM library applies accross ALL technology, and some may not have specific signa/signb inputs. You will have to instantiate the specific multiplier for the technology you are using to get full access to internal signals.