I am using MAX232 to communicate with AT89C52 under the control of PC using VB programming. The problems are: 1. How I can check if MAX232 is working or not, (by checking LED, I know the serial receiving interrupt of AT89C52 was working). 2. Why the data received by MCU are all the same? 3. Does this mean MAX232 is not working? Would you give me some suggestions? Thank you for your help. .