Sck-Internal Communication Cycle; Rs-485 Communication - Phoenix Contact SCK-C-MODBUS User Manual

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5.2.1

SCK-internal communication cycle

In the SCK-internal communication cycle, all connected measuring modules are queried in
parallel after a fixed defined request signal. The transmitted measured values are saved in
the corresponding registers. This request cycle permanently runs automatically. The baud
rate is fixed at 1200 baud. Depending on the amount of data transmitted, the cycle time is
around 1 - 2 s on average.
New measured values are therefore only available in the registers of the communication
module for the higher-level controller once a cycle has been run (refer to Figure 5-3 on
page 32).
In the event of a data transmission error between the measuring and communication mod-
ules, the data is requested again up to three times. If no valid data is available after the third
request, the device indicates an internal error.
If the module does not receive a response after 10 s, it enters "Timeout" status.
For further details on error messages, refer to "Troubleshooting" on page 75.
5.2.2

RS-485 communication

The register entries (measured data) are transmitted to the higher-level controller via the
RS-485 interface using Modbus RTU.
A unique address is set on the communication module for module and data assignment.
The DIP switches inside the device are used for this. The procedure for setting the module
address is described in "Installing the SCK-C-MODBUS communication module" on
page 49.
Table 5-1 Modbus settings
Protocol Modbus RTU
Valid addresses 1...247
Default setting: 0 (invalid address, must be changed)
Baud rate Default setting: 9600 bps
Parity Default setting: none
Stop bits Default setting: 1
Code 8-bit binary
Function code Function for reading the SCK-MODBUS measured values. All mea-
sured values are stored in a 16-bit word.
The module address is set to "0" by default and must be changed. Communication is not
possible when the address is set to "0". For additional information on setting the module ad-
dress, please refer to "Addressing the SCK-C-MODBUS communication module" on
page 49.
Assign appropriate addresses in the 1 ... 247 address area according to your system con-
figuration. By default, the address area from 248 ... 255 is assigned to non-stationary de-
vices and cannot be used.
SCK-C-MODBUS Solarcheck communication module
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