Basic Shift Register Circuit Simulator

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배울 내용

Chain flip-flops to form a shift register.
Distinguish SISO, SIPO, PISO, PIPO shift register configurations.
See bits propagate one position per clock edge.
Connect this to UART, SPI, and JTAG serial protocols.
Apply shift registers as delay lines and pseudo-random generators (LFSRs).

작동 원리

A shift register is a chain of D flip-flops where each flip-flop's output feeds the next one's input. On every clock edge, every bit shifts one position. This makes the register act as a delay line, FIFO, or serial-to-parallel converter, depending on how you wire the I/O.

The basic operation: bit 0 captures the serial input; bit 1 captures bit 0's previous value; bit 2 captures bit 1's; etc. After N clock edges, an N-bit shift register has fully "flushed" the serial input through all positions.

Four common configurations: - SISO (serial-in serial-out): One serial input, one serial output (after N cycles). - SIPO (serial-in parallel-out): Serial input, parallel outputs from each flip-flop. - PISO (parallel-in serial-out): Parallel load, then shift out one bit per clock. - PIPO (parallel-in parallel-out): Just a register, no shift.

Shift registers are the basis of many serial protocols — UART, SPI, JTAG — where data is transmitted bit-by-bit on a single wire and reassembled on the receive side.

단계별로 시도해 보세요

위 임베드에서 입력을 설정한 후, 예상 결과를 읽고 직접 확인하세요.

1

Serial in = 1 Clock = rising

예상: Bit 0 = 1, others shifted right

관찰 포인트: Serial input is captured into bit 0; bit 0's previous value moves to bit 1; etc. Each clock edge shifts the chain by one.
2

Serial in = 0 Clock = after 4 edges

예상: After 4 zeros, register clears

관찰 포인트: Sustained 0 input — after N (= width) clock edges the register is fully flushed to all-zeros.
3

Serial in = 1 Clock = after 4 edges

예상: Register fills with 1s: 1111

관찰 포인트: Sustained 1 input — register fills bit-by-bit until all positions are 1.
4

Serial in = alternating 1 0 1 0 Clock = running

예상: Pattern propagates through register

관찰 포인트: Watch the alternating pattern shift through. After 4 cycles the register holds 1010 (or 0101 depending on phase).

사용된 구성 요소

실제 응용 사례

Serial communication (UART, SPI, JTAG). Transmit-side uses PISO; receive-side uses SIPO. The serial wire carries one bit per clock; the shift register reassembles bytes.

Display drivers. LED matrix and 7-segment chips often use SIPO shift registers to expand a few SPI lines into many output bits.

Pseudo-random generators. LFSRs (linear feedback shift registers) use a shift register with XOR feedback to produce pseudo-random bit sequences.

Pipeline delay lines. A shift register can introduce N cycles of delay to align signals between fast and slow paths.

Serial test patterns. Built-in self-test (BIST) uses shift registers to inject test patterns and capture results sequentially.

자주 묻는 질문

Why are shift registers useful for serial-to-parallel conversion?

Serial buses transmit one bit per clock; the receiver needs to reassemble them into multi-bit words. A SIPO shift register collects N bits over N clocks, then presents them all in parallel — exactly the conversion needed.

What's the latency from serial input to all-bits-loaded?

N clock cycles for an N-bit shift register. After N edges, the first input bit has propagated to the last position, and the register holds N bits of data.

Can I shift left and right?

Yes — bidirectional shift registers have a direction control input. Each flip-flop's D input becomes a 2-to-1 MUX that picks the previous bit (shift left) or next bit (shift right). Bidirectional registers are common in DSP and graphics.

How is an LFSR different from a basic shift register?

An LFSR (linear-feedback shift register) feeds the output through XOR with one or more middle bits back to the serial input. The XOR creates a pseudo-random bit sequence with maximal period 2^N − 1 (for properly chosen tap positions).

What's the maximum clock speed of a shift register?

Limited by the slowest flip-flop's clock-to-Q + setup time. Modern CMOS shift registers run at multi-GHz speeds; specialty serial transceivers run faster with custom flip-flop circuits and clock recovery.