Change a variable to the opposite?

[Hylan]

I want to connect a BCD thumbwheel to my board. However, instead of 1001 = 9 which is what the thumbwheel outputs, I need 0110.

I'm not sure why the circuitry is like this but I was wondering if there was a simple command to flip a whole variable or what the best way to do this would be?

Thank you.

[HenrikOlsson]

Untested, but give it a try:


For i = 0 to 3
BCD_Value.0[i] = ~BCD_Value.0[i]
NEXT

/Henrik.

[Hylan]

I came up with:

For I = 0 to 3
if BCD_In.0[I] = 0 then
BCD_In.0[I] = 1
else
BCD_In.0[I] = 0
endif
next I

But yours is much simpler!
Perfect.
Thank you.

[Megahertz]

BCD_Value=BCD_Value ^ $0F

[Hylan]

Megahertz,

If I understand yours correctly, you're raising the value to the power of 15? How did you come up with 15? Is that a function of the 4 bits? So if it is an 8 bit variable what would the value be?

I just want to understand the logic behind it.
Thank you

[SteveB]

That is an "exclusive OR" (XOR) with a byte of 00001111. So when you input 00001001, it will return 00000110.

Here is the truth table on page 79 of the manual.


A B A ^ B
0 0 0
0 1 1
1 0 1
1 1 0
If only A or only B is 1, then result is 1.
The ^ operator is commonly used to invert selected bits:

[Acetronics2]

Hi,

... :rolleyes:

Holy Manual ... $ 3.1.14 ...

Alain

[Megahertz]

That is an "exclusive OR" (XOR) with a byte of 00001111. So when you input 00001001, it will return 00000110.

Here is the truth table on page 79 of the manual.


A B A ^ B
0 0 0
0 1 1
1 0 1
1 1 0
If only A or only B is 1, then result is 1.
The ^ operator is commonly used to invert selected bits:

This would my my answer as well.

[Hylan]

Doh! Since you posted the truth table, you are correct that I did not RTFM. Before my original post I tried to but didn't know where to look. Now I do and since most of the code uses binary I used:
BCD_In = BCD_In ^ %11111111

Thank you for the pointers and help!

[falingtrea]

Is BCD value 9 the only value that needs translation? Could you actually need a BCD to grey code translation?

[ardhuru]

If your variable is always going to be 4 bits, the complement would be got by variable(comp) = 15-variable.

Regards,

Anand