Barrel shifter design example n data inputs, n data outputs Control inputs specify number of positions to rotate or shift data inputs Example: n = 16 DIN[15:0], DOUT[15:0], S[3:0] (shift amount) Many possible solutions, all based on multiplexers
Multiplexers (mux) Select one of n sources of data to transmit on a bus. Eg. Put between Processor’s registers and ALU A 16-bit processor where 3-bit field specifies on of 8 registers. The 3-bit field is connected to the select inputs of an 8-input, 16-bit mux.
Dual-Priority Encoder A priority encoder identifies not only the highest but also the second-highest- priority asserted signal among a set of 8 request inputs.
Parallel Cascading Comparators 74x85: serial cascading scheme, delay of propagating the cascading signals through a cascade of comparators. 74x682: Parallel approach, used to build very wide comparators. Build 24-bit comparator, using 3 74x682 PEQQ=EQ2.EQ1.EQ0 PGTQ=GT2+EQ2.GT1+EQ2.EQ1.GT0
8 bit Comparator B0 A1 B1 A2 B2 A3 A0 B3 74x85 ABIN ABOUT B0 A1 B1 A2 B2 A3 A0 B3 74x85 ABIN ABOUT B0 A1 B1 A2 B2 A3 A0 B3 B4 A5 B5 A6 B6 A7 A4 B7 +5V AB Most Significant bitsLeast Significant bits
Mode-dependent Comparator Design a c.c. whose inputs are two 8-bit unsigned binary integers(X,Y), and a control signal(MIN/MAX). The output is an 8-bit unsigned binary integer Z, such that Z=min(X,Y) if MIN/MAX=1; Z=max(X,Y) otherwise