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CP 523
Protocol Errors
The protocol can detect errors caused by incorrect behaviour on the part of the link partner and
errors caused by disturbances or interference on the line.
In both cases, an attempt is first made to transmit or receive the message frame without error by
initiating a retry. If this is still impossible after the maximum number of attempts has been made
(or if another error occurs), the protocol aborts transmission or reception. An error code is entered
in the coordination byte and the CP goes to the idle state.
7.2
Prerequisites for Operation in Communications Mode
The following conditions must be met for operating the CP 523:
1. Settings on the peripheral device
The settings on the peripheral device must agree with the parameter setting data for the CP 523. If
your peripheral device is transmitting data at 2400 baud, for example, you must also set this baud
rate for the CP 523.
Note:
•
See 3.4.2 for configuration examples with terminal diagrams.
•
See 2.6.2 for details of the serial interface.
•
Setting the CP 523 parameters in Communications mode is explained in 7.3.
2. Setting the CP 523 parameters
There are two ways of setting the CP 523 parameters:
•
Store the parameter setting data on a memory submodule in DB 1.
Initialize the memory submodule with a programmer in offline mode
•
Transfer the parameter setting data in the user program after power-up or recovery of power.
The restart organization blocks are used for this purpose.
No memory submodule is required.
You must specify the following parameter setting data:
•
Parameters for the interface to the peripheral device (baud rate, type of interface, handshake
mode ...)
•
Specifications pertaining to the XON/XOFF protocol (optional)
•
Parameter setting data for data transfer in Communications mode (message frame length,
end-of-text character)
•
Correction value for the integral clock (optional)
Note:
If the CP 523 and its communications partner have different restart characteristics, data may be
lost during the restart phase. Check that your peripheral device is ready to receive before you
send data.
EWA 4NEB 811 6044-02a
Communications Mode
7-7
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