51 single chip microcomputer ROM and ram

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Tips ： The following is the main body of this article , The following cases can be used for reference

One 、51 Program memory structure of single chip microcomputer

1. internal structure

The program memory inside the single chip microcomputer is used to store the program when the single chip microcomputer is working , There is a special one inside the single chip microcomputer 16 Bit program counter （PC), The program to be executed by the SCM at the next moment is ROM Address location in space , You can store 64Kb The size .

Program memory can be divided into on-chip program memory and off chip memory , Different single-chip computer models have different on-chip program memory space .

for example 8051 SCM chip has 4Kb Of ROM, When the control line takes 0 when ,PC Before accessing 4kb Space is in the film ROM; When the control line is 0 When ,PC The access is off chip ROM.

2. Of program memory 7 A special address

51 After the MCU is reset ,PC The content is 0000H, It is the starting address of the system program .

51 There are... Inside the single chip microcomputer 6 Broken source ,6 The descriptions and addresses of the interrupt sources are as follows ：

Only interval between interrupt sources 8 Storage unit , This is not enough to store the interrupt program , So this is the interrupt entry address , Then there is the interrupt service function .

Two 、51 Data memory of single chip microcomputer

Data storage （RAM) Store the data needed during the operation of the single chip microcomputer and the temporarily generated data .
It is physically divided into on-chip RAM And off the film RAM（ Off slice RAM It's through 16 Bit address bus access , So off the film RAM It's also 64kb）.

1. On chip data storage

The manufacturer defines different task blocks according to different task requirements and requirements , As shown below ：

Working register group ： Altogether 32 Bytes , Also known as general purpose registers , For temporary deposit 8 Messages , The working register group is divided into 4 Two groups , Each group has R0-R7 altogether 8 Data information .
Bit addressing area ： Altogether 16 Bytes ,128 position , Each bit in this area can be used in the way of location , this 128 Bit will reassign the working address .
commonly RAM Area ： User programming can be used RAM, Of course , Unused space of the first two units , Users can also use it .
Stack area and stack pointer ： First in, then out 、 A storage area managed on a last in first out basis

A function call is a stack operation , As shown in the figure below ：

To implement the stack “ First in, then out , After the first out ” Data processing ,51 A stack pointer is set inside the MCU SP.

special function register ： Dedicated to control 、 Manage on-chip arithmetic logic unit and other functional modules , The user can directly set the value for the special function register when programming .51 SCM internal includes PC , 19 A special function register , As shown below ：
CPU Special register ： accumulator A(E0H), register B(F0H), Program status register PSW(D0H), Stack register SP(81H), Data pointer DPTR(82H、83H)

2. Off chip data memory

51 Inside the MCU RAM When there's not enough space , Just expand off chip through the bus ram, It can be extended at most 64KB.

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