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If no occupants have indicated their presence, then the Philips Dynalite control system will switch off the lighting and report this back to the BMS so that the aircondition plant can also be automatically shut down. If reducing the bit rate is not an option, then you could try an RS-232 to RS-485 converter at both ends. Why use a RS232 - RS485 /RS422 converter? Some of these converters can convert from RS232 to both RS485 and RS422 however many standard models only has one of the protocols. The local and remote must share a common ground, so all serial cables include at least one ground conductor. This was done since this protocol is a very common bit format used with serial communications. Most newer consumer electronics comes with an USB, Firewire or other high-speed communication port, however a lot of industrial and commercial equipment, both old and new, is made only with a RS485 or RS422 serial communications port. RS485, also known as TIA/EIA-485 is a standard serial communications protocol defining the electrical characteristics of a serial converter, drivers and receivers for use in balanced RS485 digital multipoint systems.

EIA-485 only specifies electrical characteristics of the driver and the receiver. In contrast to EIA-485 (which is multi-point instead of multi-drop), EIA-422/V.11 does not allow multiple drivers but only multiple receivers. This is a method for connecting multiple RS485 devices with each other over a two-wire network. These USB to RS485 converter and USB to RS422 adapters are most often used for connecting a RS485 or RS422 device to a personal computer. USB to RS485 is known for its multi-drop characteristics, meaning you can use USB RS485 for connecting multiple RS485 devices in a two-wire network. A RS232 - RS485 converter is often used in industrial data acquisition and control applications where multiple serial devices communicate with each other through a converter. A RS232 - RS422 converter is a 4-wire, full-duplex, differential protocol with multi-drop capabilities and a recommended distance limit of 4000ft. ANSI/TIA/EIA-422-B is the American national standard for the RS422 protocol.

Just because a protocol is used with a particular implementation of RS-232 or RS-485, RS485 standard does not mean it is part of the standard. The most important thing to keep in mind when choosing a USB RS485 converter or USB RS422 adapter is if you need a standard or industrial strength USB to RS485 converter or USB to RS422 adapter and whether it needs to be isolated or non-isolated. For example you need to consider the noise level in the environment surrounding the serial converter. Some of these converter / adapter units can convert only USB to RS485 or USB to RS422 but others can convert both RS485 and RS422 at the same time. USB to RS422 is often used for extending a RS232 wire by using a USB to RS422 adapter at each end of a RS232 wire. Usually a RS232 - RS485 converter is the preferred way to establish multi-point networks when working with RS232 devices.

With RS485, you can have multiple PC's and multiple controllers on one bus, so that one PC can send a command to change a setpoint,and another PC can send a command to send back data, etc. Remember that all devices on the bus must have a unique unit address, so that only the addressed unit will respond. The advantage of the RS485 protocol is that this it can transfer data over longer distances, up to 4000 feet, and have up to 32 nodes per single network, and it can be used for multi-point networks where multiple serial devices are setup in a bus network. This way you can extend the RS422 signal for up to 4000 feet. Since it uses a differential line over twisted pair (like EIA-422), it can span relatively large distances (up to 4000 feet or just over 1200 metres). The RS485 converter interface uses two wires for communication, one for transmitting and one for receiving data, which is referred to as a half-duplex communication converter. RS-485 is inherently half-duplex.