HEIDENHAIN TNC 410 M Technical Manual page 406

The ready signals from the power supply units are collected in the adapter
module and transmitted to the control. If a ready signal is missing, the
control cannot determine which of the inverter systems has failed to send
the ready signal.
Supply bus X69a/b:
The dc-links to be monitored must be evaluated. The present system
architecture allows monitoring of only one dc-link's voltage and current. The
dc-link with the greater load or the more critical components should be
monitored and, the respective power supply module must be connected to
X69a. The other power supply module must be connected to X69b in the
same way.
Diagnosability:
The information given above also applies to diagnosability. The control is
only able to diagnose power supply units, such as the UVR 140D, if the
supply bus (X69) of the UVR 140D is connected to X69a of the adapter
module. The power supply unit connected to X69b cannot be addressed by
the system diagnosis function.
5-V power supply X74:
The 5-V power supply must be routed from the power supply unit that has
been connected to X69a to the control.
6 – 80 HEIDENHAIN Technical Manual for Inverter Systems and Motors