17 registers
- 1. What good are registers? • Flip-flops are limited because they can store only one bit. – We had to use two flip-flops for our two-bit counter examples. – Most computers work with integers and single-precision floating- point numbers that are 32-bits long. • A register is an extension of a flip-flop that can store multiple bits. • Registers are commonly used as temporary storage in a processor. – They are faster and more convenient than main memory. – More registers can help speed up complex calculations. • We’ll discuss RAM next time, and later we’ll also see how registers are used in designing and programming CPUs.
- 2. shift registers types • Serial-in to Parallel-out Serial-in to Parallel- out • Serial-in to Serial-out • Shift registers with parallel load
- 3. A basic register • A 4-bit register from Logic Works is on the right, and its internal implementation is below. – This register uses D flip-flops. – All the flip-flops share a common CLK and CLR signal.
- 4. Shift registers with parallel load • We can add a parallel load, just like we did for regular registers. – When LD = 0, the flip-flop inputs will be SIQ0Q1Q2, so the register shifts on the next positive clock edge. – When LD = 1, the flip-flop inputs are D0-D3, and a new value is loaded into the shift register, on the next positive clock edge.