Rockwell Automation 1734-485ASC POINT I/O ASCII User Manual - Manual (Page 22)

Publication 1734-UM009B-EN-P - July 2003
1-12 Installing the ASCII Module
Cyclic and Change of State I/O
The Cyclic and Change of State (COS) connections initiate a
DeviceNet message (production) every time the connection timer
(EPR) expires. They report the most current data in the ASCII
module’s serial port receive buffer. In addition, the COS sends a data
string each time a new serial input is received from the external serial
device. This initiates the data transfer upon receipt of the delimiter or
an overflow at its serial port.
The format of the message is the same as for a Poll response. Each
message is handled in the same fashion, with respect to string
delimiters, overflows, etc., regardless of which connection mechanism
is used.
The purpose of these connections is to send data from the ASCII
modules to the scanner without a direct command from the Master,
thus conserving network bandwidth. The COS connection provides
the Master with the current data as fast (or faster) than a Poll
connection. The COS/Cyclic mechanism automatically activates when
the connection is created.
The COS and Cyclic connections are mutually exclusive per DeviceNet
definition - that is, you cannot use both of them at the same time. You
can use each one, however, in conjunction with a Poll connection.
Setting Up the DeviceNet I/O Connections
It is useful to first set up your serial link before setting up your
connection. To set up the communications with your network
configuration tool, it is necessary to know the connection input and
output sizes. Instructions for setting up your serial connection are
provided above. See Table 2.3 for receive and transmit sizes.
The input and output sizes are computed from the transmit size and
the receive sizes plus selected options. These sizes are defined in the
parameter object of your device.