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Solution:
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Division
There is no easy way to divide numbers with a PIC. So 250/5 = ? The easiest way to achieve the same result is to turn the question around and ask “how many times do I have to multiply the 5 to get 250. If the program is working with 8 bit numbers, the procedure is as follows:
- Multiply the lower number by 128.
- Check if the total is higher or lower that the higher number.
- If the total is lower or the same, add 128 number to the results register and subtract the total from the higher number.
- If the total is higher, add nothing to the results register and do not subtract anything from the higher number
- Repeat this procedure with 64, 32, 16, 8, 4, 2 and 1.
With the above figures of 250/5:
- 5 times 128 is 640. This is higher than 250 so take no action.
- 5 times 64 is 320. This is higher than 250 so take no action.
- 5 times 32 is 160. This is lower than 250 so add 32 to result and subtract 160 from 250 to leave 90.
- 5 times 16 is 80. This is lower than 90 so add 16 to result and subtract 80 from 90 to leave 10.
- 5 times 8 is 40. This is higher than 10 so take no action.
- 5 times 4 is 20. This is higher than 10 so take no action.
- 5 times 2 is 10. This is the same as 10 so add 2 to result and subtract 10 from 10 to leave zero.
- 5 times 1 is 5. This is higher than zero, so take no action.
The result register contains 32 plus 16 plus 2, which equals 50 and 250/5 also equals 50. It should be noted that this method will always round down when an exact division is not possible.
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