Taking the ‘high’ road
So, what is high level interfacing? When control systems or devices interact with each other at a communication or ‘protocol’ level it is referred to as high level interfacing or integration. Specific control messages are sent by a transmitting device using a protocol (or communication language) understood by a receiving system or device. The transmitting devices not only send messages, but the messages can change according to the specific action required to be taken by the receiving device.
The process can be somewhat complex, and is usually more difficult to implement than low level integration, but usually provides a more flexible solution.
High level interfacing of systems or devices generally requires a degree of commonality between them as a starting point:
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• Both systems need to support a common physical method of transporting messages from one to the other. This may be a hard wired data connection, such as an Ethernet cable connection, or it could be wireless connection such as WiFi.
• Both systems need to be capable of understanding a common protocol or language used to send and receive messages.
There are many common methods of physically transporting messages in control systems, among them being RS232, Ethernet and WiFi. There are also many common protocols used, such as serial, the protocols commonly used in RS232 communications, and TCP/IP used in Ethernet and WiFi communications.
The Clipsal C-Bus system offers a range of products which enable high level interfaces to an external system or devices, including via serial RS232 and TCP/IP via Ethernet.
Getting the systems talking
Once both a common physical connection and a common protocol between the systems have been confirmed, the next step in the high level interfacing process is to establish how to program one system to transmit specific messages that the other system will understand and respond to. Individual manufacturers who promote high level integration of their systems or devices usually publish a protocol document to enable this. The installer will need to understand the structure of specific manufacturer’s protocols before beginning to make the systems ‘talk’. When the protocols are understood, the installer will typically use the control systems software tools to program the send and receive messaging according to specific application requirements.
High level interfacing using RS232
Serial RS232 communication is a point to point method of communication. That is, two devices have their serial ports directly connected together via a multi-core data cable. In its simplest form this comprises of a three wire connection – a ‘data transmit’ connection, a ‘data receive’ connection and a ‘common connection’. The ‘data transmit’ connection of one device connects to the ‘data receive’ connection of the other, and vice versa. Information from a sending device (generally called a ‘serial string’) is transmitted to the receiving device in a protocol or language that is mutually understood by both devices. Some serial protocols also include acknowledgement messages to confirm they have received a message and it has been understood. Many serial protocols also allow one system to interrogate another system to establish the state of specific devices. For example, following the initial connection of a security panel to a third party system via a serial RS232 connection, the third party system may send a message asking the security panel what state each of the security zones is in (i.e. ‘OK’ or ‘Alarm’ state), if the security panel is armed or disarmed and maybe the status of the backup battery and ac power connection.
Many security panels offer this ability to integrate to third party systems at a high level. Most will at least include a serial RS232 connection which offers a connection between the control system such as C-Bus and the security panel.
High level interfacing using Ethernet
Many electronic devices and system components now include an Ethernet connection, which enables a device to exist on a computer network. Some of these devices have the capability of using this Ethernet connection to interface to other devices at a high level. One of benefits of having devices connected and communicating on a Local Area Network (LAN) is that this network serves multiple purposes. For example, some computer LAN-based media players can have media content streamed to them from a LAN-based server as well as being controlled through the same physical connection via a high-level interface to an external control device. Ethernet devices readily support multiple connections from different devices and are capable of having multiple ‘conversations’ simultaneously.
Ethernet based control can use many different protocols, the two most common being TCP/IP (Transport Control Protocol/Internet Protocol) and User Datagram Protocol (UDP).
TCP/IP allows a point to point connection between two devices. One device is configured as a ‘Server’ while the other is a ‘Client’. The server waits for a connection request from a Client device on a specific Ethernet port number.
The client will attempt to contact the Server on that port (much the same way as someone may try to call you on a specific phone number). Once the connection is made, messages can be sent and received by both the server and client.
Ethernet-based UDP communication broadcasts a message to the network for all connected devices to hear. Devices can respond to messages should they chose. Unlike TCP/IP, UDP has no method for acknowledging that a specific message was received and acted upon.
Overall, for those installers who have never been involved in high-level interfacing of systems previously, caution is required! The world of high level integration is often difficult and time consuming; research, reading and bench testing before rolling a solution out to client are all essential. However, if implemented properly the results of high level interfacing in a residential control system can be very beneficial – a ubiquitous control solution for the home owner with all horrible technical stuff well hidden!
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