An automation field device comprises a first, a second, and a third connection pin; and a field device electronics designed to be operated either in a two-conductor mode or in a three-conductor mode. The field device electronics have an energy supply unit designed to provide internal energy supply exclusively by means of the fed current in the two-conductor mode. In the three-conductor mode, an additional auxiliary current is to be fed to the field device electronics via an additional single-wire line connected to the third connection pin, and the energy supply unit is also designed to provide the internal energy supply via the fed current and the fed additional auxiliary current. Furthermore, the field device electronics are designed to use the additionally fed auxiliary current for internal energy supply only if the current fed by means of the two-wire line is not sufficient for the internal energy supply.

A received-data writer of a network unit records first data in a first data area when a flag is set indicating that a write is allowed, and records second data in a second data area. The first data are data for which data consistency is to be guaranteed among received data that is received from the first slave station and a second slave station, and the second data are data for which real-timeliness is to be guaranteed among the received data. A first transferrer of a CPU transfers the first data recorded in the first data area to a first storage at an interval of a first transfer period when the flag is set indicating that a read is allowed. A second transferrer of the CPU transfers the second data recorded in the second data area to a second storage at an interval of a second transfer period.

A received-data writer of a network unit records first data in a first data area when a flag is set indicating that a write is allowed, and records second data in a second data area. The first data are data for which data consistency is to be guaranteed among received data that is received from the first slave station and a second slave station, and the second data are data for which real-timeliness is to be guaranteed among the received data. A first transferrer of a CPU transfers the first data recorded in the first data area to a first storage at an interval of a first transfer period when the flag is set indicating that a read is allowed. A second transferrer of the CPU transfers the second data recorded in the second data area to a second storage at an interval of a second transfer period.

An automation field device comprises a first, a second, and a third connection pin; and a field device electronics designed to be operated either in a two-conductor mode or in a three-conductor mode. The field device electronics have an energy supply unit designed to provide internal energy supply exclusively by means of the fed current in the two-conductor mode. In the three-conductor mode, an additional auxiliary current is to be fed to the field device electronics via an additional single-wire line connected to the third connection pin, and the energy supply unit is also designed to provide the internal energy supply via the fed current and the fed additional auxiliary current. Furthermore, the field device electronics are designed to use the additionally fed auxiliary current for internal energy supply only if the current fed by means of the two-wire line is not sufficient for the internal energy supply.