Design of microcontroller emulator based on SST89C54/58

1 Overview

　　SST89C54/58 (referred to as 89C54/58) is a multi-purpose 51 series microcontroller launched by the American SST Company. It integrates a 20 kB/36 kB SuperFlashE'PROM program memory, which is divided into BLOCK0 (16kB/32kB) and BLOCKl ( 4kB) two pieces. Among them, BLOCKl can be mapped to the highest or lowest end of the 64kB storage space, and it can be invisible to the program counter. Due to its unique advantages in storage structure, 89C54/58 is very suitable for use as a microcontroller emulator.

2 Program storage structure of SST89C54/58

2.1 Memory structure

　　The memory block BLOCK0 in the 89C54/58 chip occupies the storage space from 0000H to 3FFFH/7FFFH, and BLOCKl occupies the storage space from F000H to FFFFH. The 89C54/58 storage structure is shown in Figure 1.

　　When EA#=1, BLOCK0 is always visible to the program counter and is used for code access; BLOCK1 code access is achieved through the special function registers SFCM, SFCF, SFAL, SFAH, SFDT and SFST. . When SFCF[7]=1, BLOCK1 is visible.

2.2 Memory remapping (Re-mapping)

　　The memory remapping function of 89C54/58 makes the system interrupt vector area still available when programming BLOCK0 (ordinary 8051 series microcontrollers do not have this feature). 89C54/58 provides 4 memory remapping methods. The number of memory remapping is controlled by MAP_ENCl: 0). When MAP-


3 Design of microcontroller emulator based on SST89C58

3.1 Introduction to design principle

　　The emulator circuit design is shown in Figure 2 Show. In the figure, U2 is the serial communication interface chip MAX232, and U1 is 89C54/58. The monitoring program of 89C54/58 communicates with KEILC51 through the PC serial port to realize the real-time simulation function.

3.2 Loading of the emulator monitoring program

　　The 89C54/58 emulator monitoring program SoftlCE (Softwareln-CircuitEmulator) provided by SST can be loaded through the BSL (Boot-Strap Loader) provided by SST or through a third-party program that supports SST89C54/58 device writes.

3.3 Introduction to emulator performance

　　The microcontroller emulator based on 89C54/58 has all the functions of a general emulator except that it does not support serial port emulation. Combined with KEIL software, the simulation design of most microcontroller application systems can be completed.

　　Its specific performance is as follows:

(1) IntelHEX format files can be downloaded.
(2) Support assembly and C51 source code debugging.
(3) Support online assembly.
(4) Supports single-step (Step) function.
(5) Supports StepOver function.
(6) A maximum of 10 fixed breakpoints and one temporary breakpoint can be set.
(?)Supports reading and writing data memory.
(8) Support reading and writing program memory.
(9) Support reading and writing special function registers.
(10)Support reading and writing ports.
(11) With IAP (1n-Application Programming) function.

3.4 KEIL software and settings

　　KEIL C51 is a Windows version of the 8051 series microcontroller development kit launched by the German KEIL company. It can be used to compile C source programs, assemble source programs, link and locate target files and libraries, create HEX files and debug target programs. , and is embedded with the RTX51 real-time operating system, which can simplify the design of complex multi-task real-time application systems. When cooperating with the 89C54/58 emulator, the settings in the KEIL development environment are as follows:

(1) Create a project and select the SST microcontroller SST89C54/58.
(2) Select "Options for, Target 1/ from the menu.
(3) In the "Options for Target, Targetl" window, select to use KEILMonitor-51Driver, as shown in Figure 3.
(4) Double-click the Settings key in Figure 3 to set the target The parameters are shown in Figure 4, and the target program can be compiled and debugged.

4 Conclusion

　　In summary, due to the unique memory structure of SST89C54/58, in addition to being used as a general-purpose 51 microcontroller, 89C54/58 only needs to be equipped with a small number of peripherals The circuit can be made into a 51 series microcontroller simulator. Combined with the powerful KEIL software, it provides a real-time simulation development environment for microcontroller engineers and can complete the design of most microcontroller application systems. Detailed design information can be obtained from the SST company website www. sst.com download.