X74_L85

4-Bit Expandable Magnitude Comparator

X74_L85 is a 4-bit magnitude comparator that compares two 4-bit binary-weighted words A3 - A0 and B3 - B0, where A3 and B3 are the most significant bits. The greater-than output, AGBO, is High when A>B. The less-than output, ALBO, is High when A<B, and the equal output, AEBO, is High when A=B. The expansion inputs, AGBI, ALBI, and AEBI, are the least significant bits. Words of greater length can be compared by cascading the comparators. The AGBO, ALBO, and AEBO outputs of the stage handling less-significant bits are connected to the corresponding AGBI, ALBI, and AEBI inputs of the next stage handling more-significant bits. For proper operation, the stage handling the least significant bits must have AGBI and ALBI tied Low and AEBI tied High.

Figure 11.2 X74_L85 Implementation XC3000, XC4000E, XC4000X, XC5200, Spartan, SpartanXL

Figure 11.3 X74_L85 Implementation XC9000