5/05 won't update S:13

Firejo said:

I’ve got a SLC5/05 (Series C, Firmware 11) and I’m trying to use the S:13 register. I’m using an MUL block multiplying an “N” register by 2.97 needing to use the results that are supposed to be in S:13. But they aren’t. Anybody ever come across this? I know the S:13 won’t update when using a float but according to everything I’ve read (and been told) anytime you use a math function the results are stored in S:13/14 as well as where the function block puts it.

Click to expand...

Well, I have never really used S:13/S:14 for anything. However, reading through the Instruction Reference, it specifically states that they will not change for a Floating Point Operation. The example you give of 2.97 is the definition of Floating Point.

Stu....

Like Stu said, the math register isn't used for floating point multiplication. The value in the N register is fetched from memory, converted into an IEEE754 float, and then multiplied by the 2.97 float. The result is a float, not an integer. Even if the target is a N file the processor first performs a floating point multiply and then converts it to an integer. If it were to save anything in S:13/14 the bit pattern would be that of a IEEE754 float and the integers values in S:13/14 would be meaningless.

If you want to use S:13/14 then multiply the N address by 297 and then do a double divide (DDV) by 100.

The info on the "float" fixed the problem. I had to take a different approach (multiplying by 297 then dividing by 100 didn't work) but I was able to get the S:13 register to do what I needed it to do.
Thanks all!

Firejo said:

The info on the "float" fixed the problem. I had to take a different approach (multiplying by 297 then dividing by 100 didn't work) but I was able to get the S:13 register to do what I needed it to do.
Thanks all!

Click to expand...

Care to share your solution. It may help someone else in the future.

---------+-MUL----------+

         |          N7:0|

         |           297|

         |       GARBAGE|

         +--------------+



---------|-DDV----------+

         |          100 |

         |          N7:1|

         +--------------+

didn't work? If this is a 5/05 and not a Mircrologix which has 32 bit capabilities then it should have worked (use L files on MLs) What exactly were you wanting then?