说明：  基于at89s51单片机系统利用专用以太网控制芯片REL8019AS实现以太网接口。没有附加硬件原理图，已经在keil c中编译通过。
(at89s51 microcontroller-based system using a dedicated Ethernet control chip to achieve REL8019AS Ethernet interface. No additional hardware diagram, in keil, c compile.)