Question

The function, ‘data bus tristated’ is performed when

(a) CS(active low) = 1

(b) CS(active low) = 0

(c) CS(active low) = 0, RD(active low) = 1, WR(active low) = 1

(d) CS(active low) = 1 OR CS(active low) = 0, RD(active low) = 1, WR(active low) = 1

The question was posed to me during an online exam.

The question is from PIO 8255 (Programmable Input in chapter Basic Peripherals and their Interfacing with 8086/88 of Microprocessor

Answer 1

The correct choice is (d) CS(active low) = 1 OR CS(active low) = 0, RD(active low) = 1, WR(active low) = 1

For explanation I would say: The data bus is tristated when chip select pin=1 or chip select pin=0 and read and write signals are high i.e 1.