A Design of USB Download Line for AT89S52 Single Chip Microcomputer

1 Introduction

With the continuous development and update of single-chip microcomputer technology, the number of single-chip microcomputer chips supporting ISP or IAP is increasing day by day. The program download of this type of single-chip microcomputer chip adopts the download line method. The level used in this serial program download method is TTL level, which is very safe for the single-chip microcomputer interface. Single-chip microcomputer manufacturers recommend using the ISP program download method. For example, the AT89S5X chip supports the ISP function, and the AT89S5X chip replaces the AT89C5X chip.

On the other hand, the writing of the program of the single-chip microcomputer has also evolved from using a burner to write the program directly from the computer using a download line. The download line is the connection line that writes the single-chip microcomputer program in the computer to the single-chip microcomputer chip. The connection interface between the download line and the computer can be divided into a serial port download line, a parallel port download line, and a USB interface download line. The level used in this serial program download method is TTL level, which is safer for the single-chip microcomputer interface and the single-chip microcomputer chip. At the same time, the program writing method using the download line does not require the single-chip microcomputer to be removed from the application circuit every time, which saves time and is completely reliable.

From the perspective of computers, computer technology is changing with each passing day, and the external interfaces of computers are also constantly changing. The main external interfaces of computer external devices are serial interfaces, parallel interfaces and USB (Universal Serial Bus, USB) interfaces. The Universal Serial Bus (USB) has the characteristics of high speed, flexible and convenient use, and has become the standard configuration of computers, and is in the trend of increasing external interfaces of computers. In order to adapt to the development of modern computers, it is imperative to use a download cable with a USB interface.

However, different microcontrollers have different download cables, and generally speaking, they have different download software and hardware drivers. These software and programs have different versions as the functions are improved and operated. This causes the users of the download cables to constantly update the software, and also requires users to not only replace the download cable when changing the microcontroller, but also to be familiar with the new download software. For this reason, if a download cable that does not require download software or a download software with unified operation can be designed, the operating efficiency of the microcontroller program download can be greatly improved. It is even more necessary to research and develop a universal download cable for microcontrollers with a USB interface that does not require download software.

2 Hardware Design

2.1 Design Concept

In order to be compatible with traditional download cables, one way is to connect a USB to parallel port (or serial port) cable to the computer, and then connect a traditional download cable. In the market, many USB to parallel port cables are dedicated to printers. It is not an emulated parallel port, but an emulated USB printer, and cannot be used to connect a parallel port download cable for program download. USB to serial port is different, because it truly simulates a serial port on the computer, and general programming software can read and write to this serial port.

Another way is to develop a separately developed USB programmer, whose functions include USB interface and download cable (some also have programmer and other functions). The internal structure of some USB programmers is a USB to serial port chip that converts to a serial port and then connects to the subsequent programming circuit. This method has the same principle and connection as a separate USB to serial port plus a download cable.

No matter which download cable is used, corresponding drivers and download programs are required. Of course, these download cables also support functions such as online simulation.

In order to achieve the goal of not needing to install the download line driver in the computer, after the download line control system is debugged, the computer system can use the system's own USB driver to implement the program to read and write the download line. This not only ensures that it can be used universally on all computers, but also realizes that there is no need for a dedicated download program in the computer. The program can be written into the microcontroller by simply copying, pasting or other file copying operations like disk operations.