I have a problem with regards to the design of a controller board that will interface 32 individual slave devices to a PC. I need to have two UARTS to serve to communication ends. The controller board acts as the master of 32 slaves set to monitor a certain parameter. The MCU used in the slave board is AT90S8515. With 32 slaves, i need to implement a serial bus line for lower cabling costs. But we had a problem using the RS485 implementation. When a single slave is connected to bus, it responds, but when another slave is added, neither of them replies to the command sent by the master MCU from the controller board. Does anyone of you had previous working designs using RS485 bus implementation which i could learn from? I also had problem implementing the 2 uSarts of the megaMCUs. The other USART is for the bus line, while the other is for the serial communication with the PC. We encountered that problem 2 years ago using ATMEGA161. but i dont know with the latest mega versions of the AVR having two USARTs.
Hope to hear from you guys soon. Thank you very much.