Expansion Methods of Single Chip Microcomputer System

　　As a most basic system, it should include program memory, data memory, keyboard, display and other circuits. In the measurement system, it also includes analog-to-digital converters and digital-to-analog converters. Due to its good scalability, the MCS-51 series of single-chip microcomputers can form a compact independent system according to the specific requirements of the system.
　　Before designing the system, comprehensive consideration should be given to issues such as the resources required by the system and the processing speed, and then the resources of the system should be allocated.
　　The memory of the MCS-51 single-chip microcomputer is divided into program memory and data memory. The program memory has a 64K addressing range independent of the data memory. When designing, devices with built-in program memory should be used as much as possible. According to the capacity of the program, devices with built-in 4K or 8K program memory can be selected. After reset, the program pointer of the MCS-51 single-chip microcomputer is 0000H, and the addresses of the five interrupt entries are 0003H, 000BH, 0013H, 001BH, and 0023H. Therefore, jump instructions should be arranged at 0000H and the entry address units of various interrupts respectively.
　　The data memory of the MCS-51 microcontroller includes internal and external data memory. The use of the internal memory should be considered in the order of stack, bit operation unit, and data unit. Sufficient units should be reserved for the stack. When using subroutines, interrupts, and stack operation instructions, the stack pointer will be affected. When estimating the stack capacity, the situation where the stack is used in large quantities due to the call of subroutines and the nesting of interrupts should be considered. In the MCS-51 microcontroller, 20H~2FH of the internal RAM are specified as 128 bit addressing units, and bit operation instructions can be executed on these bits. Therefore, when allocating memory, the flag type units should be allocated in this area. The data memory is generally allocated between 30H and the stack, and 00H~1FH are the R0~R7 units of the four zones. If the internal data memory cannot meet the requirements of the system design, the external data memory can be expanded through the P0 and P2 ports. The addressing range of the external data memory is 64K, but because the I/O address uses the memory mapping addressing method, the allocation of memory units and the allocation of I/O units should be considered uniformly.
　　The expansion of peripheral devices should be considered in the following order. If there are I2C and SPI bus devices in the peripheral interface and there is no special requirement for the communication speed, the bit operation method of P1 port can be used to simulate the serial interface. Other interfaces can be assigned addresses according to needs and unified consideration of memory addresses.