考虑具有字节可寻址存储器的处理器。假定所有寄存器，包括程序计数器(PC)和程序状态字(PSW)，均为2字节大小。从存储器位置(0100)16实现主存储器中的堆栈，并且该堆栈向上增长。堆栈指针(SP)指向堆栈的顶部元素。 SP的当前值为(016E) 16 。 CALL指令有两个字，第一个字是操作码，第二个字是子例程的起始地址(一个字= 2字节)。 CALL指令的实现如下：
• Store the current value of PC in the stack.
• Store the value of PSW register in the stack.
• Load the starting address of the subroutine in PC. 紧接CALL指令提取之前，PC的内容为(5FA0) 16 。执行CALL指令后，堆栈指针的值为
(A) (016A) 16
(B) (016C) 16
(C) (0170) 16
(D) (0172) 16答案： (D)
解释：
The current value of SP is (016E)16
The value of SP after following operations is asked
in question
• 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 becomes (016E)16 + 2 = (0170)16
• 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 becomes (0170)16 + 2 = (0172)16
• Load the starting address of the subroutine in PC.
The Load operation doesn't change SP.
So new value of SP is (0172)16 这个问题的测验