If you looked at the RS-485 signal on an oscilloscope you'd see that the signal varies between approximately +12 and -7 DC volts.Only one device is supposed to "talk" on the bus at any given time but all devices can listen.All devices on the system are connected to a data "bus", which basically means that the "A" wires from all devices are connected together and the "B" wires from all devices are connected together.Other characteristics of RS-485 communication include: These data wires are labeled "A" and "B" (or sometimes D+ and D-) and the polarity of each wire relative to the other determines whether the data bit is a 1 or a 0. Unlike serial interfaces that have separate Transmit (TX) and Receive (RX) wires, RS-485 uses two "differential" data wires for sending and receiving data. If you're familiar with the RS-485 standard you can skip the next section, otherwise I'd recommend giving it a quick read to get the gist. The first thing you need to know is that Pentair systems use an RS-485 interface for serial communication between connected devices, operating at 9600 baud (8/N/1). The good news is finding the cause of these problems isn't rocket science and involves no black magic.
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