Download File

Communication Basics
3.2.2
Failure / Warning Response Message
a.) Transmission Failure
However if the transmission of the message fails or the checksum is wrong then
there is no responded message. The sender has to synchronize itself via timeouts!
Please note, that no message is sent only in case of transmission errors, i.e. the
receiver gets a message with erroneous checksum or an undefined message
code. If the command executed fails, this has to be handled via messages
described below.
b.) Command Execution Failed
If the transmission is ok, but the command execution fails, the receiving device
will indicate the failure with the following kind of message:
Command
Message Length
Data Returned
0xFF
Chksum
0xC1
0x01
0x09
0x00
0xFF
0xFF
Group
Code
Message
Code
Low Byte
High Byte
E.g. return status etc.
0xFF
0xFF
Sum of all bytes
before
+ 0xC0
The group code is changed by a logical OR operation with 0x80 to indicate, that
it’s a response message.
An additional change by a logical OR operation with 0x40 (thus resulting in an OR
with 0xC0 = 0x80 + 0x40) indicates a failure or a warning of the requested
command.
Note:
The response message may not have the same length as the original message!
12
pco.edge Low Level Description V1.01 © PCO AG, Germany