The difference between Elan MCU and MCS-51 MCU

The assembly language of Elan microcontroller is very similar to that of MCS-51 microcontroller, but the two have completely different architectures.

My summary is, first look at the stack structure. The MCS-51 MCU stack is opened in the RAM space, and the user is required to estimate the stack usage according to the program call situation, and then define the stack pointer's top address. When the user reads and writes to change the stack area data, the program will run away. The stack of Elan and PIC MCUs has an independent fixed depth, and the user cannot directly read and write to the stack area. Only when a program call occurs, the address of the protection scene will be pushed into the stack, so it will not run away, but the depth is still limited, so it is not advisable to nest too many function calls.

1. The internal structure of Elan MCU is the same as that of PIC MCU. The bus structure of MCS-51 MCU is von Neumann type. The computer takes instructions and data in the same storage space, and the two cannot be performed at the same time; while the bus structure of PIC MCU is Harvard structure. The instruction and data space are completely separated, one for instructions and the other for data. Since the program and data can be accessed at the same time, the data throughput rate is improved. Because the Harvard dual bus structure is used in PIC MCU, one difference from common microcontrollers is that the program and data bus can use different widths. The data bus is 8 bits, but the instruction bus bits are 12, 14, and 16 bits respectively.

2. The instruction fetching and execution of the MCS-51 microcontroller adopts a single instruction pipeline structure, that is, fetching one instruction, executing it, and then fetching the next instruction; while the instruction fetching and execution of the PIC adopts a dual instruction pipeline structure. When one instruction is executed, the next instruction is allowed to be fetched at the same time, thus realizing single-cycle instructions.

3. All registers of the PIC microcontroller, including I/O ports, timers and program counters, are in RAM structure and can be accessed and operated in one instruction cycle; while the MCS-51 microcontroller requires two or more cycles to change the contents of the register.