L
Hi,
I am a student who's working on project that needs to communicate a PC (master) with a microncontroller based system (slave) through RS485. I've made some research on the Internet and got this:
The conversion from RS232 to RS485 is supposed to be done by a MAX232 which converts the signals (Tx, Rx and RTS) to TTL levels and then a SN75176B converts the TTL signals to RS485 levels. The RS485 bus is terminated on both sides (at this point there are only two devices communicating) with a 100 Ohm resistor between the two lines of communication and two bias resistors of 470 KOhm.
The software at the master uses the RTS signal to release the bus so that the slave can use it to send data (half-duplex, no parity, 2400 bauds).
The slave is controlled by ATMEL's AT89C51 microcontroller using its serial port for the communication.
At this days I finished implementing the system but the communication between master and slave doesn't seem to work even at short distances of about 1 meter. Do you have any idea of how to "debug" the system or how to find out what the problem is?
Thanks a lot,
Leo Palacios Garcia
I am a student who's working on project that needs to communicate a PC (master) with a microncontroller based system (slave) through RS485. I've made some research on the Internet and got this:
The conversion from RS232 to RS485 is supposed to be done by a MAX232 which converts the signals (Tx, Rx and RTS) to TTL levels and then a SN75176B converts the TTL signals to RS485 levels. The RS485 bus is terminated on both sides (at this point there are only two devices communicating) with a 100 Ohm resistor between the two lines of communication and two bias resistors of 470 KOhm.
The software at the master uses the RTS signal to release the bus so that the slave can use it to send data (half-duplex, no parity, 2400 bauds).
The slave is controlled by ATMEL's AT89C51 microcontroller using its serial port for the communication.
At this days I finished implementing the system but the communication between master and slave doesn't seem to work even at short distances of about 1 meter. Do you have any idea of how to "debug" the system or how to find out what the problem is?
Thanks a lot,
Leo Palacios Garcia