ABB S800 I/O Manual page 21

Section 1 Introduction
CI840 Fieldbus Communications Interface (FCI)
The CI840 Fieldbus Communication Interface (FCI) module is a configurable
communication interface which performs operations such as signal processing,
gathering of various supervision information, OSP handling and configuration of
I/O modules. The FCI connects to a controller by way of the PROFIBUS-DPV1
fieldbus.
CI840 is designed for redundant applications. One CI840 works as a primary FCI
and the other as a backup. Both FCIs supervises each other. If a fault occurs in the
primary FCI, it results in an automatic switch over to the backup CI840.
The FCI has one PROFIBUS-DPV1 interface and uses a PROFIBUS-DP cable with
a total length of up to 1200 meters (1312 yards). Up to 32 stations can be configured
on one segment. The station address sets by rotary switches that select the address
on the fieldbus in the range of 01 to 99, in redundant configurations 
1 to 62.
The FCI modules are mounted on a Module Termination Unit TU846 or TU847.
TU846/TU847 are DIN rail mounted and have connections for input power,
PROFIBUS, service tool and two rotary switches for station address selection.
TU847 with CI840 are used for single I/O applications and TU846 with CI840 are
used for redundant applications.
An I/O Station can consist of the FCI modules, ModuleBus Modems and the I/O
modules. The FCI is the bus-master on the S800 I/O ModuleBus and communicates
with the S800 I/O modules. It is a pure "slave station" on PROFIBUS-DPV1 which
is controlled by a master station.
I/O Station modules are mounted on DIN rails and are connected by the ModuleBus.
Figure 5
and connected to the Optical ModuleBus Port TB842.
modules mounted on TU846 and connected to the Optical ModuleBus Port TB842.
3BSE020926-600
shows the FCI modules mounted on a Module Termination Unit TU847
Product Scope
Figure 6 shows the FCI
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