3.6    EXOR gate
 
FIGURE 1.9    EXOR gate symbol
 
 
inputs,
               x            y
output,
z
               0            0
 0
               0            1
 1
               1            0
 1
               1            1
 0
 
TABLE 1.8    Truth table for EXOR gate.
        EXOR actually the abbreviation of exclusive OR. The EXOR gate available in the 74 series is 7486. There are also four EXOR gates packed in this IC chip.

        More information regarding the TTL 74 series gates and ICs could be found in the Manufacturer's Data Book (TTL Data Book).
 

4.0    Combinational Circuit.

FIGURE 1.10
        Combinational logic circuits are constructed by interconnecting various logic gates together to implement a particular circuit function. The combinational logic circuit in FIGURE  1.10 using many gates can also be easily represented in a logic truth table as given in TABLE 1.9.
 
 
   P             Q               R
S
   0              0                0 
   0              0                1 
   0              1                0 
   0              1                1 
   1              0                0 
   1              0                1 
   1              1                0 
   1              1                1
                     1 
                     1 
                     1 
                     1 
                     0 
                     0 
                     0 
                     1
TABLE 1.9    Truth table for combinational circuit in FIGURE 1.10.
        The circuit in FIGURE 1.10 can also be implemented using all NAND gates only. The equivalent NAND gates implementation is given in FIGURE 1.11.
FIGURE 1.11    NAND gates implementation of combinational circuit in FIGURE 1.10.