Lantronix MSS4 MSS User Guide - Page 41

MSS User Guide 4: Configuration RS-485 Configuration Note: This section applies to MSS models MSS-VIA and MSS4 only. The RS-485 standard allows a serial connection to be shared like a "party line." As many as 32 devices can share the multidrop network. Typically, one device is the master and the other devices are slaves. There are a few important things to note about RS-485 networking with the MSS. ‹ MSS-VIA allows for a serial connection on one port. MSS4 allows for a serial connection on all four ports; specify the port when entering RS-485 commands. ‹ The MSS can be used in either two-wire or four-wire mode. Refer to the following sections to determine which mode to use. ‹ The maximum RS-485 network cabling length (without repeaters) is 4,000 feet. Lantronix recommends the use of shielded twisted-pair cabling. Note: A large number and variety of protocols run over RS-485. However, the MSS does not convert or interpret serial data. It only moves data between serial and Ethernet. Any RS-485 protocol will have to be implemented by host software either on the end device or running internally using the Software Development Kit (SDK) . See 7:Pinouts for information about the RS-485 DB25 connector. To enable RS-485 mode on the MSS, enter the Change RS485 Enabled command. RS232 mode is enabled by default. Figure 4-19: Enabling RS-485 Mode for MSS4 Local> CHANGE RS485 PORT 2 ENABLED Figure 4-20. Enabling RS-485 Mode for MSS-VIA Local> CHANGE RS485 ENABLED Two-Wire Mode In two-wire mode, the MSS operates in half duplex: one pair of wires shares transmit and receive signals, and an optional third wire can be used for shield/ground. The main advantage of using two-wire mode is reduced cabling costs. Figure 4-21: Example Two-Wire Mode Network On a two-wire RS-485 network, the MSS must turn its transmitter on when it is ready to send data and then off a certain period of time after the data has been sent so that the 4-8