HONEYWELL 05704-A-0121 ISS.03 QUAD RELAY INTERFACE CARD - 5704 Instructions

The 5701 and 5704 control systems provide a complete solution for the operational and engineering requirements of a multi-channel fire and gas detection system. Each control card within the rack system provides sensor drive, signal acquisition, gas concentration display and comprehensive alarm facilities for one or more fire or gas sensors. The MODBUS Interface facility extends the capability of the control system by providing an external computer system with monitoring and control functions for every gas sensor or fire detector connected to the rack. The operation and alarm integrity of the System 57 is not affected by the MODBUS Interface. The digital data link uses a bi-directional 8-bit asynchronous serial connection that is configurable for baud rate, parity and stop bits. Two different modules are available, one supports both RS485 and RS422 electrical interface standards and the other supports the RS232 electrical interface standard. Depending upon the module type, system configuration and the capability of the host computer, various communication options are available as follows: Interface Transmission Dual Highway Multi-drop Mode Option Option RS485 Half Duplex Yes Yes (31 Nodes) RS422 Half Duplex No Yes (10 Nodes) RS232 Half Duplex No No The dual highway option provides a secondary or backup data link for increased communication integrity. Multi-drop configurations allow a single communication line to be shared by a number of devices reducing the number of communication ports required at the host computer. RS232 provides the lowest cost solution for connecting a single System 57 rack to a host computer. RS485 provides the best solution for multi-drop connection of more than one System 57 rack to a host computer and also gives the option of a secondary highway. RS422 is useful to provide multi-drop connection where the host computer software does not have the facility for transceiver direction control (transmit/receive/high impedance) that is required with RS485 connections.

In all cases the System 57 operates as a MODBUS Remote Terminal Unit (RTU), acting as a slave device node and transmitting data onto the communication line only in response to a request from a master device. The host computer system, typically a PLC, DCS or SCADA graphics package, acts as the master device controlling the communication system operation. The subset of MODBUS functions supported by the System 57 RTU are 02, 03, 04, 06 and 16. The MODBUS broadcast commands are not supported and will be ignored, however, global commands are available to reset all cards in the rack simultaneously. For a detailed description of the available commands and data formats refer to the System 57 MODBUS Function Reference given in Section 7. 2.2 MODBUS INTERFACE MODULE - RS485/422 2.2.1 General The RS485/422 Interface Module has two differential 5V transceivers designated channel 1 and channel 2. Each transceiver channel can be resistively terminated by setting LK1 and LK2 respectively (see Figure 1 and Section 3.4.3). The interface signals are isolated from the System 57 power supply 0V and Ground to protect the host computer against damage due to earth loops. 2.2.2 RS485 Operation An outline RS485 connection diagram is shown in Figure 4. When configured for the RS485 mode, transceiver Channel 1 is used in dual highway systems for the primary highway or the only highway in single highway systems. Transceiver Channel 2 is used only in dual highway systems where it functions as the secondary highway. Depending upon the type of installation, operation is possible over distances up to 1.2km (3900ft). In the multi-drop mode up to 32 nodes, including the host, can be connected. The terminal connections are: CH1-A, CH1-B Differential Transceiver Channel 1 (Primary). CH2-A, CH2-B Differential Transceiver Channel 2 (Secondary). DGND Isolated Data Ground. In a dual highway system the MODBUS uses, at any one time, only one of the two available highways, either the primary or the secondary. The interface automatically switches between highways when a communication failure is detected.

The highway switching process is controlled as follows:

a. The inactive highway is continuously monitored for data

communication.

b. If data communication is detected on the inactive highway, the

inactive highway is assumed to be fully serviceable.

c. If valid data communication ceases on the active highway and the

inactive highway is perceived to be serviceable, the MODBUS

interface switches between channels.

When configured for RS422 mode, transceiver Channel 1 is used for transmission from the System 57 RTU to the host computer and transceiver Channel 2 is used as a receiver for transmissions from the host computer to the System 57 RTU. Depending upon the type of installation, operation is possible over distances up to 1.2km (3900ft). Although the EIA RS422 standard specifies only point to point applications, the addressable operation of System 57 permits a modified 'broadcast' mode topology that allows multi-drop connection of up to 10 nodes. Each System 57 node is held in a high impedance state until it receives an appropriately addressed request, when it enables its transmitter for the duration of the response. The terminal connections are: TX-A, TX-B Differential Transceiver Output from RTU. RX-A', RX-B' Differential Receiver Input to RTU. DGND Isolated Data Ground