Lect 9 Register Continued Register A register is

Lect# 9 Register (Continued) Register • A register is a sequential circuit that can be set to a specific state and retain that state until externally changed. – State is a combination of bits 1

Register Design • An S-R latch is a simple 1 -bit register. – With (S)et input, latch output can be set to 1 – With (R)eset input, latch output can be set to 0. 2

Register Design • A D flip-flop can be used as a 1 -bit register – Input 0, output is set to 0 when flip-flop is clocked – Input 1, output is set to 1 when flip-flop clocked – Can consider the clock to be a load signal. – On rising edge of load signal, the data on D input line is stored in the flip-flop 3

Multibit Register • Use multiple flip-flops. Each stores a single bit. • Common load signal. d c Dd Ck Qd load d b a inputs Dc Db Da Ck Qb Ck Qa c b outputs a 4

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Shift registers Classification, basic function, uses: • Plain shift registers: – Serial-in serial-out – SISO (also first-in first-out – FIFO) – Serial-in parallel-out – SIPO – Parallel-in serial out – PISO – Parallel-in parallel-out – PIPO • Counters based on shift registers – Ring counter – Johnson counter • Shift register and feedback based circuits 9

Shift registers • • Serial-in serial-out – SISO Serial-in parallel-out – SIPO Parallel-in serial out – PISO Parallel-in parallel-out – PIPO 10

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Plain shift registers CLOCK SERIN SEROUT 12

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