8.4.7 Pin Selected Rail States Configuration

UCD90320U allows users to use up to 3 GPI pins to control up to 8 rail states. Each rail state enables and disables certain rails. This feature is useful to implement system low-power modes, such as those compliant with the Advanced Configuration and Power Interface (ACPI) specification. The Pin Selected States function can be configured under the Pin Selected States tab, as shown in Figure 24.

When a new state is presented on the GPI pins, and a rail is commanded to turn ON, it does so according to its sequence-on dependencies and delays. If a rail is commanded to turn OFF by a new state, it can be configured either immediately turn-OFF (Immediate OFF), or turn-OFF with its sequence-off dependencies and delays (Soft Off). If a rail is commanded to remain in the same ON state or OFF state, no action occurs.

The Pin Selected Rail States function is implemented by modifying OPERATION command. Therefore, in order to use this function to control rail states, the related rails must be configured to use OPERATION command in On/Off Config (shown in Figure 6).

The Pin Selected States feature always uses the first 3 configured GPI pins to select system states. When selecting a new system state, state changes on GPI pins must be completed within 1 µs, otherwise an unintended system state may be selected. See the UCD90320U Sequencer and System Health Controller PMBus Command Reference for complete configuration settings of Pin Selected States.

Figure 24. Pin Selected States Configuration Window (Global Configuration ►Pin Selected Rail States)