Design Specification - MUXADD

MUXADD consists of an input multiplexer, an adder, and a comparator. The multiplexer determines what value is added to the current score. The added value consists of the contents of the external card reader (V0-V3 declared as Card), a numeric value of +10, or a numeric value of -10.

The inputs ADD10 and SUB10 from the controller BJACK determines which value the multiplexer selects for the adder. Card is applied to the adder when ADD10 and SUB10 are high. When ADD10 goes low, 10 is added to the current score (to count an ace as 11 instead of 1). When SUB10 is low, -10 is added to the score (To count an ace as 1 instead of 11). The adder output is named score (S0-S4). The comparator monitors the card reader and generates the output is_Ace to BJACK signifying that an ace is present.