|Sept 9, 2013|
|The ASE2000 supports RS-485, but you need to purchase an external RS-232 to RS-485 adapter. ASE does not supply RS-485 hardware.|
Once you get an adapter, it is important to know how the adapter works. RS-485 is a half-duplex standard. You can send messages both ways, but only one way at a time. There are two basic adapter logic implementations for determining when the ASE2000 is transmitting and when it is receiving.
The first type senses data on the line. When it senses that the ASE2000 is sending data, it enables that side for transmission. When no data is sensed, it is enabled for reception. The second type uses RTS. RTS should be asserted when the ASE2000 is transmitting and cleared otherwise.
The communication properties page has four choices for carrier settings. The 4th entry, “Switched –RS485”, does exactly what is needed for type “2” converters. This setting will also work for type “1” converters. The “Constant” setting will also work for type “1” converters, and other settings may work sometimes, but are much more dependent on the converter type. The bottom line is to select “Switched – RS485” for RS-485 communication.
When using RS-485 for line monitoring (instead of master or RTU simulation), all communication in both directions will be received on a single input channel. If the protocol contains direction information identifying the source of the message, such as DNP3, the ASE2000 will correctly identify the direction of all messages and display them correctly. If the protocol does not contain direction information, such as Modbus, the ASE2000 will identify all messages as either from-the-master or from-the-RTU, depending on settings elsewhere in the ASE2000. In this case, half the messages will be identified correctly and half incorrectly. That is, the messages with the correct direction will be identified correctly.