Trying to figure out how to send/receive info to my H100 VFD (Page 79). I have cheap a RS485 attached to both my RaspberryPi (USB) and my VFD (Twisted pair). I am able to get some basic communication, I think, using the mbpoll Linux command. My goal is to figure out 3 commands. On/Off, Set RPM, Current RPM. Any help would be wonderful. Modbus is beyond my current skill set.

Code:
$ mbpoll -a 1 -b 19200 -t 3 -r 1 -c 4 /dev/serial/by-id/usb-1a86_USB2.0-Serial-if00-port0

Protocol configuration: Modbus RTU
Slave configuration...: address = [1]
                        start reference = 1, count = 4
Communication.........: /dev/serial/by-id/usb-1a86_USB2.0-Serial-if00-port0,      19200-8E1
                        t/o 1.00 s, poll rate 1000 ms
Data type.............: 16-bit register, input register table

-- Polling slave 1... Ctrl-C to stop)
[1]:    0
[2]:    0
[3]:    0
[4]:    0