DP master device

Master devices determine the data traffic on the bus. A master device is an active device. It sends messages without external request if it has bus access authorization.

A class 1 DP master device (DPM1) is a central controller that cyclically exchanges information with decentralized stations (the slave devices) in a defined message cycle. A class 1 DP master device may be a programmable logic controller or a PC, for example.

A class 2 DP master device (DPM2) is an engineering device, a configuration device or an operating device. A class 2 DP master device is used during commissioning, maintenance and diagnostics to configure connected devices, to evaluate measured values and parameters, or to query device states.

In multi-master mode, several master devices are connected to one bus. For example, independent subsystems can consist of one DPM1 device and one slave device each. Configuration devices or diagnostic devices can also be used as master devices.

When operating in multi-master systems, access protection is required for the inputs and outputs of the slave devices to ensure that direct access only takes place from the authorized master device. A token is exchanged to ensure access protection. The master device with the token has access permission. For all other master devices, the slave devices provide an image of their inputs and outputs, which can be read by any master device, even if it lacks access authorization.