Ok. Those are the results, but still, I'm not familiar with the nature of your project so this could be meaningless for your application.
For the filter design, input parameters are shown on next picture:
The result is filter of 12th order with coefficients
1. 0,0435401222614106
2. -0,0497007964907402
3. -0,0767048395375377
4. -0,0302227741478355
5. 0,114786730175788
6. 0,284995861384153
7. 0,361001857406659
8. 0,284995861384153
9. 0,114786730175788
10. -0,0302227741478355
11. -0,0767048395375377
12. -0,0497007964907402
13. 0,0435401222614106
Note that coefficients are symmetric around the 7th value, so you can use this fact to efficiently implement filtering. Also, consider implementing with integer types (char, short, long - signed or unsigned), since integer operations on 8051 are much, much faster than with the floating type.
On the following picture is input signal from file '1.txt':
And on the following picture is the output of the filter:
Tell us the results