Parallel port realizes ISP function of AT89S series microcontroller

1 ISP Overview

At present, technicians engaged in the design and development of single-chip microcomputers generally use the following common methods to develop single-chip microcomputer products: first, use single-chip microcomputer simulation equipment to simulate and debug hardware and software, and then use a program burner to solidify the debugged target code into the program memory of the single-chip microcomputer. In this process, the program burner is an indispensable development tool . The program burner is generally expensive, which is a considerable expense for beginners and will directly affect the enthusiasm of beginners to further learn and develop single-chip microcomputers. In addition, every time the source program is modified, the single-chip microcomputer chip must be removed from the target board, and then the updated target code is re-solidified into the single-chip microcomputer chip. In this way, the chip and circuit board will be physically damaged due to frequent plugging and unplugging of the single-chip microcomputer chip during debugging. The disadvantages of programming single-chip microcomputers with the help of a program burner are that the burning equipment is expensive, the burning operation is cumbersome, and it is not convenient to implement in-system programming (ISP). In order to overcome the above shortcomings and limitations, some new compatible products of 80C51 are designed with serial programming capabilities, that is, the hardware function of implementing "serial programming interface logic" is set inside the chip.

In recent years, ATMEL has continuously improved and launched the AT89S series of microcontrollers (including AT89S51, AT89LS51, AT89S52, AT89LS52, AT89S53, AT89LS53, AT89S8252, AT89LS8252.AT89S8253, AT891.58253 and other models) which have gradually replaced the original AT89 series and AT89C series microcontrollers. The AT89S series microcontrollers are based on the standard 80C51 and have an additional hardware function to implement the "serial programming interface logic" to support the in-system programming (ISP) of the microcontroller chip.

ISP is system online programming, which means that blank devices on the circuit board can be programmed to write the end-user code without removing the device from the circuit board. For programmed devices, ISP can also be used to erase or reprogram them. The implementation of ISP is relatively simple. The usual practice is that the program memory inside the chip can be rewritten by the software of the host computer through the synchronous serial communication interface SPI . For the single-chip microcomputer, the data sent by the host computer can be received through SPI or other serial interfaces and written into the program memory. The advantage of ISP technology is that the single-chip microcomputer can be experimented and developed without a programmer, which not only saves the cost of single-chip microcomputer development, but also avoids the trouble of frequently plugging and unplugging chips during debugging. ISP technology is the future development direction of single-chip microcomputers.

2 AT89S series MCU ISP principle

The AT89S series microcontrollers launched by ATMEL support ISP function. The AT89S52 microcontroller in the AT89S series has strong functions and high performance-price ratio. Therefore, this article uses the typical chip AT89S52 in the AT89S series microcontroller as an example to introduce the ISP principle of the AT89S series microcontroller.

The AT89S52 microcontroller has an online programming function, that is, when the RST pin is at a high level, the program download function is realized by setting or transmitting data of the three pins P1.5/MOSI (serial data input terminal), P1.6/MISO (serial data output terminal), and P1.7/SCK (synchronous clock signal input terminal). The pin diagram of the AT89S52 microcontroller 40-pin dual in-line package (DIP40 for short) is shown in Figure 1, and the serial programming interface of the AT89S52 microcontroller is shown in Figure 2.

Figure 1 AT89S52 DIP40 pin diagram

Figure 2 AT89S52 serial programming interface circuit diagram