Trouble connecting Arduino >> SN75176BP >> RS845 Device

Using Arduino Networking, Protocols, and Devices
#1

Hello,

I am experiencing some problems trying to interface with an RS485 power meter. I am using the official Modbus library, I have checked all parameters to make sure they are all right. I think the problem is due to the SN75176BP (converts RS232 to RS485) chip needing to be enabled for sending-recieving, as it is not full duplex. I have no idea where to switch between directions, as this would take a deep understanding of the library, which I do not have. Anyone else have any ideas or experience with this chip?

Any suggestions are appreciated!

#2

I've some questions regarding to your post:

  • Is your board a Master or an Slave?

I think that this controller is half-duplex like the MAX483 and its derivatives. This means that your controller must pull the RS485 transceiver DE/RE direction line. The rule of thumb is:

Your controller MUST LISTEN TO the RS-485 most of the time and SPEAK ONLY when requested.

#3

Please look at this: http://real2electronics.blogspot.com/2009/09/arduino-and-rs485-english-version.html

#4