This is a follow-up question from my previous thread regarding the sending of serial data from one 8051 to another. http://www.keil.com/forum/docs/thread4180.asp Although I have enabled to have one 8051 send out data (delayted byte by byte) while the other end recieves it by polling method, but it is unreliable. ie sometimes it can work but sometimes it cannot. Interestingly, it always work when I try it for the first time after I've downloaded the program into the 8051. Subsequently, when I reset both the 8051, the data will not be successfully recieved by the recieving end. Im quite puzzled why is this so as technically speaking, it does not make a difference as the behavoir of the program will still be the same after system reset. Am I missing out something on the hardware side?