多用户卡是连接主机和终端之间的通信控制卡，在多用户业务处理的微机中广泛使用，较常用的有四用户卡和八用户卡等。这些多用户卡主要由异步接口控制芯片（如16C450和UMB82450等）配接了MC1488和MC1489芯片，来传送和接收计算机信息。在多年的计算机维护工作中，笔者发现由于 Multi-user card is connected between the host and the terminal communication control card, widely used in multi-user business processing microcomputer, the more commonly used four user cards and eight user cards. These multi-user cards mainly by the asynchronous interface control chip (such as 16C450 and UMB82450, etc.) with the MC1488 and MC1489 chip to send and receive computer information. In many years of computer maintenance work, I found that