DESCRIPTION AND OPERATION
MODULE DATA
2 - 8
I-E96-207A
®
The COM reads a one byte value that consists of digital output
readback values and digital input values. The digital input val-
ues indicate the digital input states. Each bit corresponds to
one input; the bit value reflects the state of that input, either
open (logic 0) or closed (logic 1). Digital output readback data
reflects the output states. The COM uses this data to verify
that the outputs are correct. Each bit corresponds to one out-
put; a logic 1 indicates an active (ON) output, a logic 0 indi-
cates an inactive (OFF) output.
Status Data
Status data is an eight-bit data value that identifies the con-
troller module and indicates the default values set by the ana-
log output default dipswitch (S2/S3). The COM reads the
identification bits (four MSB) to verify the module bus commu-
nication integrity and configuration of other master modules. It
reads the default bits (four LSB) to determine the default states
set for the analog outputs in the event of a
time out
.
Module Bus
The module bus provides an 83.3 kilobaud peer-to-peer serial
communication link capable of supporting up to 32 drops. The
module bus is the process control unit (PCU) level communica-
tion bus. It is the bidirectional communication link for up to 32
controller modules and other modules in the system. Figure
shows the relationship of the communication highway and
module bus.
Communication Highway
The communication highway (Figure
) is used at the system
level. It is a unidirectional redundant system of connected pro-
cess control units (PCUs). A PCU is a group of modules com-
municating via a module bus. A maximum of 63 PCUs can be
on the loop.
Station Link
Station Link controls the serial communication between the
COM and the panel stations. It provides a five kilobaud serial
channel for up to eight control stations (IISAC01 or NDCS03)
and up to four Digital Indicator Stations (NDIS01).
Module Mounting Unit
The Module Mounting Unit (MMU) houses the modules in a pro-
cess control unit. The controller module can occupy any of the
12 slots. A controller module slides into the MMU on module
guides and is secured by two 1/2 turn captive latches. To
remove the module, turn both captive latches 1/2 turn until the
notches point away from the center of the module faceplate .
