1 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 Lect# 9 Register (Continued)

2 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.

3 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

4 Multibit Register Use multiple flip-flops. Each stores a single bit. Common load signal. DdDd CkQdQd DcDc QaQa DbDb QbQb DaDa QaQa d cba dcba load inputs outputs

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9 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

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

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12 Plain shift registers CLOCK SERIN SEROUT

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