
System Monitor
80175-01
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SERIAL INTERFACE OVERVIEW
PROTOCOLS
The 3300 Serial Interface option gives the 3300 system communication capability using either RS-
232C or RS-422A connections. The interface implements two standard protocols which are switch
selectable on the interface. The protocols are Modicon Modbus and Allen Bradley full duplex (DF1).
Each protocol possesses its own unique characteristics but the data which is transferred over each
interface link is similar. That data consists of each monitor's current values and status values.
DIFFERENCES FROM BASIC SYSTEM MONITOR
The interface option installs in the system monitor slot and rides on top of the System Monitor main
circuit board. With t h e interface installed, t h e original functions o f t h e System Monitor remain
unaltered. To supply the communications signals, the 3300 system backplane has an additional 32
pin din connector located immediately below the 64-pin din backplane connector. This connection
supplies the communications signals to and from the Power Input Module (PIM). The PIM provides
the required communications connectors.
SELECTION SWITCHES
Selection switches on the Serial Interface allow the setting of the device address and baud rate. In
addition such selections as message checking mode (cyclic redundancy check or block character
check), parity and stop bit selection, modem controls enable, and protocol mode can be set. To
identify the positions o f any 6-channel monitors in the rack, 6 switches are provided. Each switch
identifies an odd slot position which corresponds to the left side slot into which a 6-channel monitor
is placed.
SCAN METHOD
The Serial Interface uses the Data Manager Communications Processor (CP) backplane controls and
multiplexed analog d a t a signal t o receive information from t h e 3 3 0 0 monitors. I f there i s n o
Communications Processor connected to the 3300 rack, the Serial Interface generates the required
backplane control signals to scan the rack. The Serial Interface will then scan as if the rack is a full
14 position rack. If there is a Communications Processor present, then the Serial Interface gathers
data in synchronism with the Communications Processor. In this case, the Serial Interface gathers
data only from the points which are configured in the Data Manager software.
The scanning of the rack is constantly active in the Serial Interface. Data obtained from the scanning
process is deposited in a data base maintained within the interface. When a request for data is
received via a protocol message from an external device, the requested data is retrieved from the
data base, formatted and returned to the requesting device in a message response. Allen Bradley
and Modbus protocols have different message formats for requests and responses. For a complete
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Содержание 3300/01 Series
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