FieldServer FS-8700-78 Driver Manual Dart Driver Description, Performance Issues

Driver Manual

1 Dart Driver Description

The Dart Driver is designed for connection to a Data Air Coporation Dart Device.

The Dart device is a active element on a network of Data Air devices such as DAP panels. It manages the devices and provides co-ordination and supervision. In performing these duties the Dart device polls all the devices on the network for all the data. The Dart is capable of ‘echoing’ the responses from these devices on one of its RS232 ports. This driver is designed to listen passively to these echoes and store device data. In addition the driver can send messages (containing set point data, for example,) directly to individual devices on the network.

The FieldServer is connected to the RS232 serial port of the Dart. The Fieldserver can read and write but active polling must be minimized as in reduces the amount of time that the DART spends controlling the networked devices. The driver operates primarily as a passive client listening to echoes of the data being polled by the DART. The DART must be set to ‘Echo’ mode on the front panel of the Dart for the driver to operate correctly. There is no alternative to this essential but manual setup-step.

The driver may be configured very simply (See example 1 in section 4 of the manual). In addition a number of advanced configurations are possible. The manual is divided to separate the basic and advanced topics.

The driver supports the common message formats for common Data Aire devices. A list of the supported messages is provided in the manual. The driver cannot be used to configure or read the status of a DART device itself.

The information that follows describes how to expand upon the factory defaults provided in the configuration files included with the FieldServer.

1.1Performance Issues

Several factors outside FieldServer’s control make for slow communications with Data Aire devices. The Data Aire communications is based on a very low baud rate. In addition inter- message timing constraints and overhead requirements for active messages in a Dart configuration add significant time to each transaction.

When a used with a DART device, writing to a set point (or other variable) may take up to 8 seconds to complete the transaction. The results of the write will not be seen until the DART has timed-out back into control mode and echoes the new data to the Fieldserver. This could take several minutes if there are many devices on the loop and will take at least 30 seconds.

When writing continuously, with DART configurations, the minimum time interval between successive writes is 2 minutes and with non-DART configurations is 1.8 seconds.

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