80C31 是INTEL公司MCS-51系列单片机中最基本的产品，它采用INTEL公司可靠的CHMOS工艺技术制造的高性能8位单片机，属于标准的MCS-51的HCMOS产品。它结合了HMOS的高速和高密度技术及CHMOS的低功耗特征，标准MCS-51单片机的体系结构和指令系统。
80C31内置中央处理单元、128字节内部数据存储器RAM、32个双向输入/输出(I/O)口、2个16位定时/计数器和5个两级中断结构，一个全双工串行通信口，片内时钟振荡电路。但80C31片内并无程序存储器，需外接ROM。
此外，80C31 还可工作于低功耗模式，可通过两种软件选择空闲和掉电模式。在空闲模式下冻结CPU而RAM定时器、串行口和中断系统维持其功能。掉电模式下，保存RAM数据，时钟振荡停止，同时停止芯片内其它功能。80C31有PDIP(40pin)和PLCC(44pin)两种封装形式。
The MCSÉ 51 CHMOS microcontroller products are fabricated on Intel's reliable CHMOS process and are functionally compatible with the standard MCS 51 HMOS microcontroller products. This technology combines the high speed and density characteristics of HMOS with the low power attributes of CHMOS. This combination expands the effectiveness of the powerful MCS 51 microcontroller architecture and instruction set.
Like the MCS 51 HMOS microcontroller versions, the MCS 51 CHMOS microcontroller products have the following features: 4 Kbytes of EPROM/ROM (87C51/80C51BH respectively); 128 bytes of RAM; 32 I/O lines; two 16-bit timer/counters; a five-source two-level interrupt structure; a full duplex serial port; and on-chip oscillator and clock circuitry. In addition, the MCS 51 CHMOS microcontroller products exhibit low operating power, along with two software selectable modes of reduced activity for further power reductionÐIdle and Power Down.
The Idle mode freezes the CPU while allowing the RAM, timer/counters, serial port, and interrupt system to continue functioning. The Power Down mode saves the RAM contents but freezes the oscillator, causing all other chip functions to be inoperative. The 87C51 is the EPROM version of the 80C51BH. It contains 4 Kbytes of on-chip program memory that can be electrically programmed, and can be erased by exposure to ultraviolet light. The 87C51 EPROM array uses a modified Quick-Pulse Programming algorithm, by which the entire 4 Kbyte array can be programmed in about 12 seconds.
