如何做一个的LEA指令店地址？ [英] How does LEA instruction store address of A?

问题描述

这是基于关闭这个问题 LEA指令

This is based off this question LEA instruction

下面是code段我有一个关于

Here is the code segment I have a question about

.ORIG X3700
 LEA R0, A
 .....
  A .FILL X1234

@保罗R，答案应答，表示code的起源是x3700，你有12个指令，所以A的地址将是x3700 + X0C = x370C。正如你猜到了，LEA R0 ，A加载进R0的地址，这样第一个指令已经执行后R0将包含x370C。

@Paul R, the answer responder, said that "The origin of the code is x3700, and you have 12 instructions, so the address of A will be x3700 + x0C = x370C. As you guessed, LEA R0,A loads the address of A into R0, so R0 will contain x370C after that first instruction has been executed."

我同意保罗所说的第一部分，他的推理为什么A的地址是x370C。这就说得通了。

I agree with the first part of what Paul said, his reasoning for why the address of A is x370C. That makes sense.

我感到困惑的下一个部分，即LEA R0，A加载的地址复制到R0。这是对LEA指令幻灯片我参考了。 LC3 LEA ，5-23

I am confused about the next part, that "LEA R0, A loads the address of A into R0". This is the slide my reference has on the LEA instruction. Lc3 LEA, 5-23

不同于ADD和和说明，机关指令只有一个模式。（参考指定ADD两种模式，并与

Unlike the ADD and AND instructions, the LEA instruction has only one mode.(reference specifies both modes for ADD and AND.

从这个图中，LEA的第二部分，A应该PCoffset 9.但是A的值是4660（十进制）从，A X1234 .fill伪，这超出了PCoffset 9范围内，这是-256到255）。

任何人能解释这是怎么回事？我使用了错误的图作为参考？有另一种LEA模式？

From this diagram, the second part of LEA, A should be PCoffset 9. However the value of A is 4660(in decimal) from ,A .FILL X1234, which is beyond the PCoffset 9 range, which is -256 to 255).
Can anyone explain what is going on? Am I using the wrong diagram as a reference? Is there another LEA mode?

推荐答案

每当你看到一个PCoffset为运code操作

Anytime you see a PCoffset as an opcode operand

LEA R2, A    ; Loads the memory location of A into R2
             ; LEA, DR, PCoffset9

它告诉你，当你的code组装它实际上并没有将标签贴'A'到您的LEA命令。

It's telling you that when your code is assembled it doesn't actually place the label 'A' into your LEA command.

看看下面code：

.ORIG X3700     ; Not a code line in the simulator, only used by the assembler
LEA R0, A       ; Line 1, starting at x3700
HALT            ; Line 2
A .FILL X1234   ; Line 3, located at x3702
.END            ; Not a code line in the simulator, only used by the assembler

现在在模拟器机关行实际上是这样的：

Now in the simulator the LEA line actually looks like this:

1110 000 000000001    ; Opcode 1110 is LEA
                      ; 000 is our register R0
                      ; 000000001 gives us how many memory locations away A is

而这正是偏移的手段。它要求的问题A走多少的内存块是我吗？如果我们的变量'A'是太多街区那么我们会因为我们不能再present，在价值偏移得到一个错误。

And that's what the offset means. It asks the question "How many blocks of memory is A away from me?" and if our variable 'A' is too many blocks away then we will get an error because we cannot represent that value in the offset.

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