Dear ALL I want to help form your sit in following scenario. I have 5 89c51 one is master and other 4 are slave. Mater can communicate with PC through serial port and Master can be communicating with other 4 89c51.Basically I am using 4 slave for expansion of IO pins.I an not understanding that when Master communication with PC how is communication with slave because Tx and Rx is connected with MAX-232. Communication sanarios is some stream coming from PC Master Read the Stream and transmit a protocol to the slaves and slaves read the stream and targated slaves pick the information and send byte to his port . My question is when Master is communicating with PC how is communication with slaves Thanks.
You need to use two separate serial ports on your "master" 8051 - one to communicate with the PC, and the other to communicate with the "Slave" 8051s. Not really, if they are on the same board (or in the same cage) there are many other means (IIC, SPI parallel ....) Erik