Rockwell Automation 5370 Color CVIM Communications Manual - Manual (Page 103)

Chapter 5
Using the RS–232 Ports
5–35
•
Object Field — The Object field specifies data that configures the
operation of the Color CVIM module.
In the description of each command we specify the objects that can
entered into a command.
•
Flags — This optional field specifies outputs on the local I/O board or
specific blocks of data.
•
Data Field — Contains data.
After receiving a DF1 data packet, the Color CVIM module validates the
Block Check Character.
Note: The block check character is a technique used to check the integrity of
of data packet. BCC are explained in the next section.
Depending upon whether or not the BCC is validated, the following will
occur:
•
If the BCC is not acceptable, the Color CVIM module will reply with a
DLE NAK (Negative Acknowledgment) character and discard the data
packet.
•
If the command has an acceptable BCC the Color CVIM module will
reply with a DLE ACK (Positive Acknowledgment) character and try to
execute the command.
After receiving a data packet and validating the BCC, one of the following
will occur.
•
If data packet has a valid BCC but the Color CVIM module cannot
execute the command the Color CVIM module will discard the data
package. No message is returned. The host should be set to time out after
waiting for a response.
•
If the command can be executed, the Color CVIM module will respond
with any returned data packets.
Command Structure (cont’d)
ACK/NAK, BCC Characters