Using the CPx8xx USB Bus Coupler
Bus Couplers of type CPx8xx are integrated into Beckhoff Panel PCs. Various different I/O terminals are connected through these Bus Couplers. In addition to the standard I/O channels of a Panel PC, further I/O terminals can be connected through which, for instance, special keys, LEDs, rotary switches or similar items can be operated. When a Panel PC is used as a CP Link 3 client there are different options for accessing the client's integrated USB Bus Coupler from the host PC:
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- via standard Ethernet
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- via RT Ethernet
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- via standard Ethernet
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- via RT Ethernet
The differences between the different varieties is explained in the following table:
Possible release of the USB Bus Coupler outputs:
The USB Bus Coupler built-in to the client expects a certain time interval, in which it receives data to write to its outputs. In the standard configuration of a CPx8xxx Bus Coupler this time interval is 100 ms. If this time interval cannot be met, the outputs of the Bus Coupler are released. Depending on the usage type of the USB Bus Coupler, in practice under certain conditions, the time interval may not be met and the outputs of the Bus Coupler released. Generally, this seldom if ever happens, but cannot be ruled out altogether. Reasons for this are the type of network connection of the Bus Coupler integrated into the client to the host PC or the operating system architecture of the host PC. If the I/O access of the host PC takes place via a standard Ethernet connection, during data exchange with the Bus Coupler, a lot of small data packets per cycle must be sent consecutively over the IP connection. Depending on the network load and the client CPU load sending of these packets can take longer than the time interval defined.
To be certain that these outputs are not released under any circumstances, I/O access from the host must be implemented by RT Ethernet, or the I/O access must take place on the client PC itself. If I/O access takes place on the client itself this does however increase the configuration effort as the inputs and outputs of the Bus Coupler cannot be used directly on the host PC, but must be made available by ADS or network variables.
Cycle time for the data exchange with the Bus Coupler
The recommended cycle time for the data exchange with the terminals of a USB Bus Coupler is 50 to 80 milliseconds. The following options are available for ensuring compliance of the cycle time during data exchange with the Bus Coupler:
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- Tasks with variables that are linked with the I/O channels of the Bus Coupler are configured with a cycle time of more than 50 milliseconds.
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- Tasks with variables that are linked with the I/O channels of the Bus Coupler may be configured with a cycle time of less than 50 milliseconds, although in this case it is necessary to activate the so-called Async Mode for the Bus Coupler:
