Rockwell Automation 1775-KA PLC-3 Communication Adapter Module User Manual - Manual (Page 39)

Installation
Chapter 2
2Ć27
Communication Mode
This option determines whether the RS–232–C port of the 1775–KA
module can operate in a half–duplex (polled) or full–duplex (unpolled)
mode. Select full– duplex for point–to–point communication through the
RS–232–C port. Select half–duplex if the 1775–KA module is installed
as a slave station on a multipoint modem link. If you make no selection,
the 1775–KA selects the full– duplex (unpolled) mode by default.
Even Parity
This option determines what kind of parity check is used for all
communications through the RS–232–C port. If option 5 EVEN PARITY
is selected, the 1775–KA module will test for even parity in all
communications through its RS–232–C port. If this option is not
selected, the module will not perform any parity checking. At power–up,
the PLC–3 disables the even parity option by default.
Send Embedded Responses
This option determines whether or not the 1775–KA module will be able
to send embedded responses through its RS–232–C port. Responses are
acknowledgments (ACKs or NAKs) to messages received from other
stations. An embedded response is one whose characters are transmitted
between the bytes of a regular message. In this way, the response to a
previously received message is transmitted along with a new message. At
power–up, the PLC–3 disables the embedded responses option by default.
The 1775–KA module can combine with the PLC–3 processor to form a
backup system. System backup is described in greater detail in the
PLC–3 Programmable Controller Backup Concepts Manual (pub. no.
1775–6.3.1). The following discussion is an overview of system backup
and the role of the 1775–KA in various backup procedures.
There are two possible backup configurations for the 1775–KA module:
Two 1775–KA modules in the same PLC–3 controller
One 1775–KA module in a primary PLC–3 controller and another
1775–KA in a backup PLC–3 controller
The first configuration provides backup for the 1775–KA module itself.
Here, both 1775–KA modules are always active, and both are independent
stations on their communication network. Therefore, each 1775–KA
Backup Configurations