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: