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.
this is too vague to answer 1) what EXACT derivative do you use 2) are the 5 controllers on the same board Basically I am using 4 slave for expansion of IO pins maybe another approach would be better, have you checked PCA9556/57 or PCA9534/54/54A16-PCA9535/55 from Philips or the PSD chips from ST micro? Erik