Asynchronous Data Transfer - Strobe Control

In asynchronous transfer source and destination use different clocks; data transfer is coordinated by a control signal called strobe - a single pulse that validates data.

1. Source-Initiated Strobe:
Source places data on data bus and after a brief delay (to allow data to settle) asserts STROBE. Destination on detecting strobe, captures data; data must remain valid while strobe is active.

Timing: Data valid → Strobe ↑ → Destination loads data → Strobe ↓ → Data invalid

2. Destination-Initiated Strobe:
Destination asserts strobe to request data; source on detecting strobe places data on bus. Destination captures data when source indicates data valid.

Block diagram: Source (Data + Strobe line) → Data Bus → Destination with strobe line directly connecting control.

Disadvantages

1. No Handshake / No Acknowledgement: Source strobes without knowing if destination received data or was ready. If destination not ready or strobe delayed/ distorted, data is lost.
2. Timing Critical: Correct operation depends on accurate delay - data must be stable before strobe reaches destination. Variation in bus length, gate delays, or clock skew can violate setup/hold time.
3. Susceptible to Noise: Single pulse can be corrupted; no error detection.
4. No Flow Control: Cannot handle speed mismatch; fast source can overrun slow destination.
5. Not Suitable for Long Distances: Strobe and data propagation delays differ.

Hence Handshaking method (using STROBE + ACK / REQ + ACK) is preferred which provides interlocked feedback and eliminates timing constraints at cost of an extra signal and longer transfer time.