On 3/3/19 11:59 AM, Thaddeus Waldner wrote:
I plan to use the VF-s11 driver. I actually have it loading
successfully in my Hal and Ini setup and connecting to the usb-rs485
device but all that it can do so far is count transmission errors.
Modbus can be hard to troubleshoot because there is very little reply
feedback unless everything is working properly (slave ID, correct baud
rate, stop bits, parity, handshake, 7 1 E seemed to be popular way back
when, but 8 1 N these days, and reply is based solely on a time interval
after the end of the master's end of packet).
My problem is, if I understand it correctly, that the Toshiba
protocol a) uses a higher voltage than any of the standard
protocols,
RS232 uses a higher voltage (12V ?) than RS485.
b) is inverted—though I’m not sure what the implications
are of that —,
RS485 manufactures have not implemented A and B signals consistently, so
I just try to reverse them to see what happens.
and c) is single-ended instead of differential. I hope
to fix this with a few resistors and inverters.
RS232 is single ended, RS485 is balanced (A and B wires) but also may
need a signal common or ground wire to keep the common mode voltage
within reason. So 1 pair plus one wire with over all shield (grouned on
one end) seems to be the ideal cable (Belden 3106a cable, pricey). A 120
Ohm termination resistor(s) may be needed but short runs should work
without it.
https://en.wikipedia.org/wiki/RS-485
My guess is that Toshiba would tend to stick to the standard since other
devices could be on the same bus.
It looks like the VFD needs a fair amount of programming from the front
panel to get the Modbus RTU/RS484 port setup?
https://www.toshiba.com/tic/datafiles/S11_Communications_Manual_Rev.3_6565.pdf
Recently, I got three different USB to RS232 adapters and the DeTech was
the only one that mostly worked out of the box. One didn't work at all.
Another needed A and B switched and was flaky. My guess is that getting
an oscilloscope out and playing with the software and hardware
configuration might get the other two working.
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