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Digital DesignDatapath Components Figure 4.9 Right rotate example: register contents before and after the rotate, and bit-by-bit view of the rotate operation.
Digital DesignDatapath Components Figure 4.10 Above-mirror display design using shift registers to reduce the number of lines coming from the car’s computer.
Digital DesignDatapath Components Figure 4.13 A small combinational circuit maps the control inputs ld, shr, and shl to the mux select inputs s1 and s0.
Digital DesignDatapath Components Figure 4.14 Truth table describing operations of a register with left/right shift and parallel load along with the mapping of the register control inputs to the internal 4x1 mux select lines (left), and a compact version of the operation table (right).
Digital DesignDatapath Components • Step 1: Determine mux size • There are 5 operations -- load, shift left, synchronous clear, synchronous set, and maintain present value. • Step 2: Create operation table Example 4.6 Register with load, shift, and synchronous clear and set/
Digital DesignDatapath Components • Step 3: Connect mux inputs • Step 4: Map control lines • s2 = clr’*set • s1 = clr’*set’*ld’*shl + clr • s0 = clr’*set’*ld + clr Example 4.6 Register with load, shift, and synchronous clear and set.
Digital DesignDatapath Components A 2-bit adder, which adds two 2-bit numbers, could be designed by starting with the following truth table.
Digital DesignDatapath Components Figure 4.19 Why large adders aren’t built using standard two-level combinational logic -- notice the exponential growth. How many transistors would a 32-bit adder require?
Digital DesignDatapath Components 0 10 11 1 1111 1111 1111 1111 +0110 +0110 +0110 +0110 ---- ---- ---- ---- 1 01 101 10101 Figure 4.17 Adding two binary numbers by hand, column by column.
Digital DesignDatapath Components Figure 4.21 4-bit adder: carry-ripple implementation with 3 full-adders and 1 half-adder (left), and block symbol (right).
Digital DesignDatapath Components Figure 4.22 4-bit adder: carry-ripple implementation with 4 full-adders, with a carry-in input (left), and block symbol (right).
Digital DesignDatapath Components Figure 4.26 8-bit DIP-switch-based adding calculator, using a register to block spurious LED outputs.
Digital DesignDatapath Components Figure 4.27 Compensating scale: the dial outputs a number from 0 to 7 (000 to 111), which gets added to the sensed weight and then displayed.
Digital DesignDatapath Components Figure 4.28 Combinational shifters: (a) left shifter with block symbol shown at bottom, (b) left shift or pass component, (c) left/right shift or pass component.
Digital DesignDatapath Components • Example 4.9 Approximate Celsius to Fahrenheit converter. • We want to convert that temperature to Fahrenheit, again using 8 bits. The equation for converting is: • F = C*9/5 + 32 • Let’s assume that we are not concerned about accuracy, so we’ll replace the equation by a simpler one: • F = C*2 + 32 Figure 4.29 Celsius to Fahrenheit converter.
Digital DesignDatapath Components Figure 4.33 4-bit magnitude comparator: internal design using identical components in each stage (top), and block symbol (bottom).
Digital DesignDatapath Components Figure 4.35 A combinational component to compute the minimum of two numbers: internal design using a magnitude comparator (left), and block symbol (right).
Digital DesignDatapath Components Figure 4.36 4-bit up-counter block symbol. Figure 4.37 4-bit up-counter internal design. Figure 4.38 Adding 1 to a binary number requires only 2-bits per column.