Adding recirculation to a 4-bit PISO register By adding recirculating lines to a 4-bit parallel-in, serial-out register, it becomes which kind of register (in/out capabilities)?

Introduction / Context:
A 4-bit PISO (parallel-in, serial-out) shift register outputs bits serially after a parallel load. If you add recirculation (feeding the serial output back to a serial input), you extend its capability to also accept serial data and to re-use or loop data, creating more flexible in/out modalities. This question asks you to identify the resulting I/O capabilities in standard shorthand.

Given Data / Assumptions:

• Base device: 4-bit parallel-in, serial-out register.
• Added feature: recirculation path (serial feedback), possibly with gating.
• Parallel outputs are inherently available at the register stages.

Concept / Approach:
With recirculation, the device can accept serial input (via the feedback/gated serial path) in addition to its original parallel load. The stored contents can be observed in parallel (tap Q outputs) and shifted out serially. A concise descriptor is “serial-in, parallel, serial” (i.e., serial in, parallel out available, serial out available).

Step-by-Step Solution:
Original: parallel-in → serial-out (PISO).Add recirculation/gated serial path → now supports serial-in as well.Stage taps provide parallel observations → “parallel.”Thus, capabilities: serial-in, parallel (out), serial (out).

Verification / Alternative check:
Universal shift registers (e.g., 74HC194) illustrate how mode control enables serial-in left/right, parallel load, and serial/parallel outputs. A PISO with added feedback approaches this flexibility.

Why Other Options Are Wrong:

• Parallel-in, serial, parallel: Omits serial-in; not reflecting the added capability.
• Bidirectional in, parallel, series / Series-parallel-in, series, parallel: Nonstandard/ambiguous phrasing and not the common shorthand.

Common Pitfalls:

• Assuming recirculation only loops the same data but does not enable serial-in; with gating, it can accept new serial data.
• Forgetting that parallel taps are inherently available on many shift registers.

Final Answer:
Serial-in, parallel, serial