The GATE Grind

GATE 2021 IN – Question 21

Digital Electronics · Microprocessors and data acquisition · 1 mark · Multiple select

A 16-bit microprocessor has 20 address lines A0–A19 and 16 data lines. Its higher eight data lines connect to the eight data lines of a 16 Kbyte memory storing one byte at each of 16K addresses. Map the chip to contiguous memory locations occupying only 16 Kbytes. Which statements are correct?

  1. If the starting address is 80000H, the ending address is 83FFFH
  2. The active-high chip select for a starting address F0000H is $A_{19}A_{18}A_{17}A_{16}$
  3. The chip cannot map to contiguous addresses starting at 0F000H using only A19–A14 for chip select
  4. The chip cannot be interfaced because its data-bus width differs from the processor’s

Practise this question in The GATE Grind →

Show answer and explanation

Correct answer: (A) If the starting address is 80000H, the ending address is 83FFFH; (C) The chip cannot map to contiguous addresses starting at 0F000H using only A19–A14 for chip select

Explanation

A 16-Kbyte chip spans 0x4000 addresses, so 0x80000+0x3FFF=0x83FFF: A. Selecting only A19–A16 at F0000 leaves 64 Kbytes selected, so B fails the only-16-Kbyte condition. A19–A14 decode aligned 16-Kbyte blocks; 0F000 is not aligned, so C is true. An 8-bit chip can connect to one byte of a 16-bit bus, so D is false. **A,C**.