Hi,
I have 2 VFD's connected on a daisy chain to a serial port on my computer using Modbus rs485, at 19.2kbaud/s, 2stop bits, 8 data bits, no parity and slave address 1 and 2. I can communicate fine when only polling to 1 device, but when I poll 2 devices, it doesnt work, sometimes I get a successful read, sometimes I don't, and writes are never successful on the VFD's, but when only communicating to 1 device, it works without hiccups.
I've tried increasing the silent time on the VFD's from 2ms to 20ms and adding the termination resistors om the front and back of the daisy chain, both of which i think might have helped with the read sometimes but im not 100% sure.
So my local supplier tells me that his cat5 and his control cable are okay to use with modbus, I've tried both but they both give me the same problem. Is it possible that this is the problem for an application with such a short distance within 3meters? Has anyone else had this experience? Also the ground reference for rs485 interface, should it be connected with the panel ground where the VFD's are on one end via the shield wire and reference gound to the other end? On my vfd manual, it says to connect the shield to the 0V pin on the VFD side and the shield to panel ground and ground reference on the other. Which is correct?
Thanks!
I have 2 VFD's connected on a daisy chain to a serial port on my computer using Modbus rs485, at 19.2kbaud/s, 2stop bits, 8 data bits, no parity and slave address 1 and 2. I can communicate fine when only polling to 1 device, but when I poll 2 devices, it doesnt work, sometimes I get a successful read, sometimes I don't, and writes are never successful on the VFD's, but when only communicating to 1 device, it works without hiccups.
I've tried increasing the silent time on the VFD's from 2ms to 20ms and adding the termination resistors om the front and back of the daisy chain, both of which i think might have helped with the read sometimes but im not 100% sure.
So my local supplier tells me that his cat5 and his control cable are okay to use with modbus, I've tried both but they both give me the same problem. Is it possible that this is the problem for an application with such a short distance within 3meters? Has anyone else had this experience? Also the ground reference for rs485 interface, should it be connected with the panel ground where the VFD's are on one end via the shield wire and reference gound to the other end? On my vfd manual, it says to connect the shield to the 0V pin on the VFD side and the shield to panel ground and ground reference on the other. Which is correct?
Thanks!