Microsoft Office Tutorials and References

In Depth Information

**Syntax**

Caution

The TRUE in F9 of
Figure 12.4
seems surprising. With all three ar-

guments TRUE, the Exclusive Or function is returning a TRUE. This

answer is based on the actual results of XOR gates such as the

74LVC1G386 microchip. This chip first does an XOR of the first two

arguments. This results in the top Venn diagram shown in
Figure 12.5
.

The chip then cascades that resulting Venn diagram into an XOR with

the third argument. The result is that the scribbled FALSE area of the

top Venn diagram when XOR
’
d with the TRUE third argument returns a

TRUE. Electrical engineers call this a paritygeneratoror a modulo-2

adder. Although it would be difficult to continue the Venn diagram

showing the intersection of 4, 5, or 254 circles, you can imagine how the

intersection area flips to FALSE for an even number of circles and

then back to TRUE for an odd number of circles.