Central Processing Unit Q.50

0. Consider a processor with byte-addressable memory. Assume that all registers, including Program Counter (PC) and Program Status Word (PSW), are of size 2 bytes. A stack in the main memory is implemented from memory location (0100)16 and it grows upward. The stack pointer (SP) points to the top element of the stack. The current value of SP is (016E)16. The CALL instruction is of two words, the first word is the op-code and the second word is the starting address of the subroutine (one word = 2 bytes). The CALL instruction is implemented as follows:
Store the current value of PC i the stack.
Store the vale of PSW register i the stack.
Load the starting address of the subroutine in PC. the content of PC just before the fetch of a CALL instruction is (5FAO)16. After execution of the CALL instruction, the value of the stack pointer is

Answer
Comment
Array

Option : D
Explanation : The current value of Stack pointer is (016E)₁₆ The value of SP after following operations is asked in question
(1) Store the current value of PC in the stack. This operation increments SP by 2 bytes as size of PC is given 2 bytes in question. So (016E)₁₆ + 2 = (0170)₁₆
(2) Store the value of PSW register in the stack. This operation also increments SP by 2 bytes as size of PSW is also given 2 bytes.
So (0170)₁₆ + 2 = (0172)₁₆
(3) Load the starting address of the subroutine in PC.
The Load operation doesn't change SP. So new value of SP is (0172)₁₆

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