A-B 1747-BSN Backup Scanner Module

Overview

The 1747-BSN Backup Scanner Module provides a high-speed communication

channel between two modular SLC 500™ (5/02 or higher) processors. The 1747-

BSN backup system uses a set of modules, with one or more 1747-BSN modules

residing in the primary system and one or more complementary modules in the

secondary or backup system. The primary system controls the operation of

remote I/O, while the secondary system monitors communications via the highspeed

serial link (HSSL) and is available to take over control in the event of a

fault in the primary system.

The backup scanner has the capability to switch between two communication

channels. The first channel is configurable as Remote I/O (RIO) or Data

Highway Plus™ (DH+). The second channel is used to switch one RS232/485

channel in order to provide connection for electronic operator interfaces.

A backup system using the 1747-BSN modules supports up to eight BSN

modules in each processor chassis, connected by a local status link (LSL). Only I/

O residing in remote chassis is backed up. Local I/O is not backed up. Examples

of RIO and DH+ system configurations are shown in Figures 1 and 2 on page 6.

Note: During the transfer of control from one processor to

another (switchover), the output modules in the remote

chassis maintain their last state until the secondary

processor program takes control. The secondary

processor program is not synchronized with the primary program.

The 1747-BSN module provides backup functionality for the following:

• DH+ or RIO on a single pair of modules - Both may be backed up when two

or more pairs of modules are used.

• RS232 - Any RS232 device communicating with channel 0 of the SLC

controller may be backed up provided hardware-handshake lines are not

required. These ports only allow switchover of the transmit, receive and

ground wires for RS232.

Configuration Errors

The module reports the following configuration errors by flashing the fault LED:

• two 1747-BSN modules are configured with the same address

• LSL addresses are not consecutive (addresses must be numbered 0, 1, 2,etc.)

• last LSL switch is not set in the last module in the link

• last LSL switch is set in a module that is not the last in the link, or

• primary and secondary modules do not have the same configuration settings

(secondary module shows the configuration error)

Switchover Conditions

The 1747-BSN module transfers control from the primary to the secondary

processor (switchover) if one of the following fault conditions occurs in the

primary system:

• power failure

• major fault in the processor

• 1747-BSN module fault

• primary processor mode change from Run to Program

Note: In order for switchover to occur, both primary and

secondary modules must be working without faults prior

to the event that triggers the switchover.