Correct AnswerA. Input port is loaded into input latches
Quick Explanation
In strobed input operation, a LOW pulse on STB̅ tells the 8255 that valid peripheral data is present and causes the input port data to be loaded into the input latch. The corresponding buffer-full/status logic is then updated.
Detailed Explanation
Concept & Reasoning
STB̅ is an active-low peripheral handshake signal in Mode 1 input. Its falling/low action captures input data so the CPU can later read a stable latched value. Output latches are associated with output-mode handshake signals such as OBF̅, not with the STB̅ input event.
How to Solve It in the Exam
STB = strobe input → input latch.
Important Exam PointActive-low notation means LOW is the asserted condition.
Related Revision Path
This question sits in the revision path Microprocessors and Interfacing → 8255 PPI → Mode 1 Handshaking .
