Explain the use of 128 bytes lower and 128 higher RAM in AT89S52 microcontroller

The AT89S52 has 256 bytes of on-chip data memory. The high 128 bytes overlap with the special function registers. That is, the high 128 bytes have the same address as the special function registers, which are physically separated.

When an instruction accesses an address higher than 7FH, the addressing method determines whether the CPU accesses up to 128 bytes of RAM or special function register space. Direct addressing access to Special Function Registers (SFRs).

For example, the following direct-addressed instruction accesses 0a0h (P2 port) memory cell MOV 0a0h, and data uses indirect addressing to access up to 128 bytes of RAM. For example, in the indirect addressing method below, r0 is 0a0h, and the register of address 0a0h is accessed, not port p2 (which also has the address of 0a0h).

MOV @r0, data stack operations are also indirect addressing. As a result, a high 128 bytes of data RAM is also available for stack space.

Some are special function registers, and some are just ordinary RAM

AT89S52 internal RAM can be used as follows:

h 1fh is used as a working register.

H2FH is the bit register.

H 7FH is at the discretion of the user.

At 128 bytes high, it can be freely used by the user, but can only be used in indirect addressing.

Various optical memory devices are also available. The time it takes to access a particular string of data in an optical memory device can be as short as the time it takes to access data on a (magnetic) hard drive. There is a slight defect on one of the smooth mirror surfaces of the disc.

Burning a hole in the surface of the disc represents the binary number 1, and no hole in the disc indicates 0. A fired disc is an example of a "write once, read many times" round or (worm) disc. This feature makes them suitable for long-term archival storage while maintaining a high access rate.

Discs with a diameter of 12 cm have become the standard for both recording and regular PC use. These disks are called "high-density disks" or CD ROMs. A high-capacity disk that is the same size as a CD ROM, but can store enough digital information to hold for several hours is called a digital disk.

It is becoming popular. Sometimes, upon request, a mechanical device is used to extract and mount the disc from a large batch of discs. These devices are known as "jukeboxes".

3] Memory. Classify.

The storage media that make up the memory are mainly semiconductor devices and magnetic materials. The smallest unit of memory is a bistable semiconductor circuit or a CMOS transistor or magnetic material that can store a binary**. A memory cell is made up of several storage elements, and then a memory is formed by many memory cells.

4] There are several different ways to classify memory according to the performance of the storage material and the method of use. [4]

Whether this memory architecture is used in the storage cabinet or storage, and then the amount of data that can be held in this storage is very large, and it is not easy to be damaged. The AT89C51 microcontroller memory space can be physically divided into four parts:

On-chip program storage, off-chip program storage, on-chip data storage, and off-chip data storage.

The AT89C51 microcontroller internal memory is divided into four parts:

The general register group is the high area, the bit addressing area, the direct addressing area, and the indirect addressing area. The so-called four spaces are: on-chip program storage, off-chip program storage, on-chip data storage, and off-chip data storage.

The on-chip program storage area and the off-chip program storage area are uniformly addressed, so there are only three logically: the difference between the on-chip data storage area, the off-chip data storage area and the on-chip and off-chip unified addressing program AT89S51 52 MCU and AT89C51 MCU, the resources come from the network** here, please use it after the verification year.

The main differences between them are the following:

1.Pin function: The pins are almost the same, and there are variations, in AT89S51, there is a second function, that is, the second function of these 3 pins forms the interface for serial ISP programming.

2.Programming: AT89C51 only supports parallel programming, while AT89S51 supports not only parallel programming, but also ISP re-line programming.

In terms of programming voltage, the programming voltage of AT89C51 requires 12V in addition to the normal working 5V, while the AT89S51 only needs 4-5V.