Identifying the register type from its behavior Which register accepts a complete binary number serially (one bit at a time) and also shifts stored bits out one at a time?
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Aparallel-in, parallel-out
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Bparallel-in, serial-out
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Cserial-in, parallel-out
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Dserial-in, serial-out
Answer
Correct Answer: serial-in, serial-out
Explanation
Introduction / Context:Register classifications describe how data enters and leaves: serial or parallel, in and out. Matching behavioral descriptions to register types is basic digital logic literacy.
Given Data / Assumptions:
- Input arrives as a bitstream (serial).
- Output also departs as a bitstream (serial).
- No requirement for simultaneous multi-bit output.
Concept / Approach:
By definition, a serial-in, serial-out (SISO) register uses a single data line for input and typically exposes the last stage as the serial output. On each clock, data shifts one stage forward; after N clocks, an N-bit word has been fully entered or exited.
Step-by-Step Solution:
Input mode: serial → must be “serial-in”.Output mode: serial → must be “serial-out”.Therefore, the correct type is serial-in, serial-out.Verification / Alternative check:
Contrast with SIPO (serial-in, parallel-out), which would provide all bits at once; PISO (parallel-in, serial-out), which would load in parallel but shift out serially; PIPO, which does both in parallel.
Why Other Options Are Wrong:
- PIPO and PISO include parallel operation, contradicting the description.
- SIPO outputs in parallel, not one bit at a time.
Common Pitfalls:
- Confusing direction of data movement with width of the I/O interface.
Final Answer:
serial-in, serial-out