ABB DSPC 157 Communication card

It is also possible to overload the CIs by using too fast a poll rate on the OPC server. The poll variables are divided into two groups: those that have SOE or Process Historian enabled (Sequence of Events Update and Process Historian Update), and the Modbus data that does not have SOE (Global Ungrouped Tag Update). The product description for the OPC Server describes loading and timing calculations. An Ethernet link should be designed to be less than 30 % loaded.For CIs before release 3.5, allow about 3 ms per Modbus / data packet for the OPC server if the CI is not running peer to peer. If the CI is running peer to peer, allow about 6 ms per OPC packet. The non SOE Modbus data may have several packets, each update depending how the Modbus variables are distributed. Sequential Modbus addresses are the most efficient.

Interface Adapter Connectors 

Table 24 below gives a list of connectors required to interface to the CI Interface Adapter (T8153). The network statistics are available by typing 'tcp ns' on the CI diagnostic (see section 5). By waiting 10 seconds and requesting another reading it is possible to work out how many packets are passing over a 10 second period and hence the time per packet. The situation can be made worse if there are a lot of writes to the system, because they are individually passed to the Processor and can take longer.

SOE Over Modbus Protocol 

The SOE Over Modbus Protocol is defined in two parts: the definition of the Modbus registers within the SOE Address Window, and the defined interaction between the Modbus Master and the SOE over Modbus service. 7.1. SOE Address Window The SOE Over Modbus protocol operates over the Modbus addresses within the configured SOE Address Window. Modbus operations on address within this window are used exclusively for the protocol. The SOE Over Modbus service defines registers within the address space required for the operation of the protocol. Each register is accessed in the normal manner

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