8051 MCU Tutorial Lesson 9: Data Transfer Instructions

Data transfer instructions

1) Instructions with the accumulator as the destination operand

MOVA，Rn

MOVA，direct

MOVA，@Ri

MOVA，#data

In the first instruction, Rn represents R0-R7. In the second instruction, direct refers to the direct address, and in the third instruction, it is what we just talked about. The fourth instruction is to send the immediate data to A.

Let's illustrate this with some examples:

MOVA, R1; send the value in the working register R1 to A, and the value in R1 remains unchanged.

MOVA,30H; send the value in memory unit 30H to A, and the value in unit 30H remains unchanged.

MOVA,@R1; first check the value in R1, take this value as the address, and send the value in this address unit to A. If the value in R1 is 20H before executing the command, the value in the 20H unit is sent to A.

MOVA, #34H; send the immediate number 34H to A. After executing this instruction, the value in A is 34H.

2) Instructions that operate on register Rn

MOVRn,A

MOVRn,direct

MOVRn,#data

The function of this set of instructions is to send the contents of the source address unit into the working register, and the source operand remains unchanged.

MCU Instructions (II)

Data transfer instructions

(3) Instructions with direct address as destination operand MOVdirect,A Example: MOV20H,AMOVdirect,RnMOV20H,R1

MOVdirect1,direct2MOV20H,30H

MOVdirect,@RiMOV20H,@R1

MOVdirect,#dataMOV20H,#34H

(4) Instruction with indirect address as destination operand MOV@Ri,A Example: MOV@R0,AMOV@Ri,directMOV@R1,20H

MOV@Ri,#dataMOV@R0,#34H

(5) The sixteen-digit transfer instruction MOVDPTR, #data168051 is an 8-bit machine. This is the only 16-bit immediate number transfer instruction. Its function is to send a 16-bit immediate number to DPTR. The upper 8 bits are sent to DPH and the lower 8 bits are sent to DPL. For example: MOVDPTR, #1234H, after execution, the value in DPH is 12H and the value in DPL is 34H. Conversely, if we send numbers to DPH and DPL respectively, the result is the same. For example, there are the following two instructions: MOVDPH, #35H, MOVDPL, #12H. It is equivalent to executing MOVDPTR, #3512H. Comprehensive exercises:

Give the result after each instruction is executed

MOV23H,#30HMOV12H,#34H

MOVR0,#23H

MOVR7,#22H

MOVR1,12H

MOVA,@R0

MOV34H,@R1

(23h)=30h

(12h)=34h

(R0)=23H

(R7)=22H

(R1)=12H

(A)=30H

(34H)=34H

MOV45H,34H

MOVDPTR,#6712H

MOV12H, VAT

MOVR0, DPL

MOVA,@R0

(45H)=34H

(DPTR)=6712H

(12H)=67H

(R0)=12H

(A)=67H

Note: The content is represented by brackets, such as (23H) represents the value in the internal RAM 23H unit, and (A) represents the value in the accumulator A unit.

Computer exercises:

Enter DOS state and enter the directory where WAVE is located, for example D:WAVE

Type MCS51

Press File->Open. When the dialog box appears, enter a file name in Name (see Figure 2). If the file already exists in the list below, open the file. If the file does not exist, create a new file.

Enter the above program in the blank space. See Figure 4. Use ALT+A to assemble it. Use F8 to execute it step by step. During the execution, pay attention to the changes in the values ​​of the working register and the A accumulator on the left side of the screen.

The change of the value in the memory cannot be seen here, but can be observed in the following way (see Figure 5): Move the mouse to DATA, double-click, and the cursor will enter this line. At this time, you can use the up and down cursor keys on the keyboard to flip up and down to observe the change of the memory value. The data after the DATA at the front of this line represents the starting address of "a section", such as 20H now. Look at the top of the screen, the numbers from 0 to F, and the sum of the two is equal to the real address value. As shown in the figure, the values ​​of memory 20H, 21H, 22H, and 23H are FBH, 0EH, E8H, and 30H respectively.

Figure 56. After running the program, you will enter its disassembly area, which is not what we want. To start from the beginning, you can use the CTRL+F2 function key to reset the PC value. Note that you will not see the original window at this time. To see the original window, please use ALT+4 or ALT+5 to switch. Of course, the above operations can also be performed through the menu. CTRL+F2 is to reset the program, use the RUN menu. The window uses the WINDOWS menu.

This time, let's get familiar with this software. To be honest, I don't like it very much. It is not convenient to operate, but this is the only software I can use on my machine. I have no choice but to introduce a better one to netizens next time.