You will find that you get better advice from the PLCTalk community when you ask good questions. Here's some similar advice: How to Ask Questions the Smart Way.
The MicroLogix 1400 shares an ASCII string and serial port command set with the rest of the MicroLogix and SLC-500 controller family. You can learn about the ASCII command set in the online Help file, or in the ASCII instruction section of the Instruction Set Reference.
Can you post more information about your specific application ?