---
title: "Strobe versus handshake protocol"
subject: "Embedded System"
chapter: 5
key: "semester_6/embedded_system:strobe-vs-handshake"
source: https://www.bctengineer.com/q/semester_6/embedded_system/strobe-vs-handshake
site: BCT Engineering
---

# Strobe versus handshake protocol

Embedded System · Chapter 5: Interfacing

- Asked in: 2071 Bhadra, 4 marks
- Video: [Asynchronous data transfer | Strobe control | COA | Lec-50 | Bhanu Priya](https://www.youtube.com/watch?v=EHdi72VVvB4) — Education 4u
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_6/embedded_system/strobe-vs-handshake
- Whole chapter: https://www.bctengineer.com/md/semester_6/embedded_system/chapter-5

## Question

What are the differences between strobe and handshake protocol?

## Short answer

In strobe protocol, the master sends data and a single strobe pulse; the slave must read within a fixed time, with no acknowledgment, making it simple but less reliable. Handshake protocol uses separate request and acknowledge lines, allowing the master to wait for the slave's acknowledgment, ensuring reliable transfer regardless of device speed, at the cost of added complexity.

## Answer

| Point | Strobe protocol | Handshake protocol |
|---|---|---|
| Principle | The master sends data and a strobe pulse; the slave must read the data within a fixed time | The master and slave exchange request and acknowledge signals before and after the transfer |
| Control lines | One strobe (or enable) line | Two lines: Req and Ack |
| Acknowledge | None; the master does not know whether the data was received | The slave acknowledges that it received the data |
| Speed matching | Master assumes the slave is fast enough; the slave must be as fast as the strobe | Works with devices of any speed; the master waits for Ack |
| Reliability | Lower (data can be lost if the slave is slow) | High |
| Complexity | Simple, minimal hardware | More complex (extra line, state logic) |
| Typical use | Synchronous transfers to fast devices (memory read/write) | Printer (Centronics), asynchronous parallel I/O |

In a **strobe** transfer, the master puts the address/data on the bus, activates the strobe for a fixed time, and removes it. In a **handshake**, the master asserts Req with the data, the slave latches it and asserts Ack, the master removes Req, and the slave removes Ack.

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. In a strobe transfer, how does the master know the slave received the data?
   A. The slave raises an interrupt
   B. The slave sends Ack
   C. A parity bit is returned
   D. It does not; there is no acknowledge
   Answer: D. Strobe assumes the slave is fast enough; there is no acknowledge, so data can be lost if the slave is slow. (Key point: Strobe acknowledgement)

2. What is the handshake sequence?
   A. Slave sends data, then master sends Ack
   B. Master asserts Req with data, slave latches and asserts Ack, master removes Req, slave removes Ack
   C. Both set a common line high for a fixed time
   D. Master sends a pulse and removes it
   Answer: B. Handshake uses Req and Ack lines so the master waits for the slave. (Key point: Handshake sequence)

3. Which protocol suits devices of any speed and why?
   A. Strobe, because it is reliable
   B. Handshake, because the master waits for Ack
   C. Strobe, because it has fewer lines
   D. Handshake, because it is simpler
   Answer: B. Handshake is more reliable and works with slow devices, but needs extra lines and logic. (Key point: Speed matching and reliability)

## Related in Embedded System

- [Process versus thread differences](https://www.bctengineer.com/question.md?key=semester_6%2Fembedded_system%3Aprocess-vs-thread) — Embedded System, chapter 6, asked 4×
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- [Datapath versus control unit](https://www.bctengineer.com/question.md?key=semester_6%2Fembedded_system%3Adatapath-vs-control-unit) — Embedded System, chapter 2
- [SRAM versus DRAM](https://www.bctengineer.com/question.md?key=semester_6%2Fembedded_system%3Asram-vs-dram) — Embedded System, chapter 4

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