考虑具有字节可寻址存储器的处理器。假设所有寄存器，包括程序计数器 (PC) 和程序状态字 (PSW)，大小为 2 个字节。主存中的一个栈是从内存位置(0100) 16开始实现的，并且向上增长。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，第二个字是子程序的起始地址(一个字 = 2 个字节)。 CALL 指令实现如下：
• 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. 在获取 CALL 指令之前 PC 的内容是 (5FA0) 16 。 CALL指令执行后，栈指针的值为
(A) (016A) 16
(B) (016C) 16
(C) (0170) 16
(四) (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