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Technical Notes
Recommendations for DF1 Communication Settings with the DeltaV Serial Card
By Martin Berutti
Product: DeltaV Serial Drivers

This purpose of this technical note is to describe recommended settings for communication with Allen-Bradley PLCs using the DF1 driver.

IOD-1123, Allen-Bradley DF1 Driver for the DeltaV Serial Card is a proven solution for integration of DeltaV with Allen-Bradley PLCs.  We often get questions about the configuration of the driver communications and device address.  To follow are our recommendations:

A-B DF1 - Half-duplex vs Full-duplex

It is not always clear when DF1 full-duplex protocol can be used and when one needs to use DF1 half-duplex.  The A-B documentation on DF1 describes full-duplex as a peer-to-peer protocol whereas half-duplex is a master/slave protocol.

The driver always communicates as master/slave.

Although the driver supports Full Duplex and Half Duplex communications, we recommend the use of the default communication mode of Full Duplex with BCC Error Checking.  To select this communication mode leave SpecialData3 of the dataset configuration to the default value of 0.

In certain cases half-duplex, CRC, can be used.  However, not all device data types support this.  The IOD-1123 driver supports the full command set for both full-duplex and half-duplex communications.  If the user has a choice the full-duplex command set should be used.

Furthermore, the link layer of the DeltaV serial interface is always master/slave in that the interface module always initiates a message transaction.  The interface module and driver do not support peer-to-peer communication or token passing.

DHPlus Device Addresses

Device addresses are important for both multi-idrop communications through a KF2 and direct point-to-point.  In point-to-point communications, the driver uses the device address, but the PLC ignores it.  With the use of the KF2 gateway, the Device Address is necessary to get a response from the appropriate PLC.  Remember the device address is the address of the PLC, notthe communication gateway.  The Allen-Bradley address is octal and needs to be converted to decimal before entering as the device address.