RST_OUT_N for fieldbus interfaces

The netX 90 enables realising the most popular fieldbus interfaces on the market by connecting the appropriate physical layer circuits to XM0 (see netX 90 Design-In Guide). As illustrated in Figure 1, whenever a transceiver circuitry is used that does not explicitly feature an enable input signal, Hilscher recommends using a transistor circuit as switch in the Tx line to avoid any disturbance on the bus during a power cycle. The RESET# signal, for instance, can be controlled by a separate Power-on Reset (POR) circuit or the RST_OUT_N pin of the netX 90.

Figure 1: Example CANopen interface

The RST_OUT_N pin of the netX 90 is a 3-state output that can be used to reset any external device. During reset, the output is high impedance and the level determined by the external pull up or down resistor until the software releases the connected device from reset. As illustrated in Figure 2, the output driver can be enabled and set to the desired level in software by using the hardware configuration tool of the netX Studio CDT.

In this particular case in Figure 1, a pull-down resistor is required at the RESET# signal and it is advisable to consider a gate resistor. The enabled output driver of the RST_OUT_N pin has to be set to high (see screenshot).

Figure 2: Hardware configuration tool netX Studio CDT