4.1 V_DDIOx Ready Voltage Monitor

The primary voltage monitoring circuit is implemented on all versions of the MVIO module (PIC and AVR) is the V_DDIOx Ready voltage monitor. The MVIO voltage domain is designed to be independent of V_DD, meaning that depending on the application, V_DD or V_DDIOx may ramp up or down independent of each other. Additionally, either one of the voltage supplies may lose and regain power while the other maintains its state without any issues. The MVIO module has a minimum required supply voltage needed for the internal level shifting circuitry to work properly which is specified in the electrical specifications section of each device data sheet.

The V_DDIOx Ready voltage monitor provides a way to monitor each available MVIO supply independent of V_DD and determine when it meets or exceeds the minimum voltage required for proper operation. Alternatively, it can also be used to determine when the MVIO supply voltage has dropped below the required minimum voltage for the level shifters to operate correctly during operation. Depending on the device family, the status of the V_DDIOx voltage monitor is provided using a dedicated interrupt flag or status bit.

Figure 4-1 illustrates how the V_DDIOx Ready voltage monitor behaves on the PIC18-Q24 device family as the V_DDIO2 voltage supply ramps up and down. On this specific device family, the V_DDIOx Ready status bit and associated interrupt flag will be set when the respective V_DDIOx supply voltage is below the minimum required value, indicating that the V_DDIO2 voltage domain is not ready for use. Once the V_DDIO2 supply voltage has reached the minimum required voltage level for operation, the RDY status bit of the VDDIO2CON register and the VDDIO2RDYIF interrupt flag will be cleared in hardware, indicating that the V_DDIO2 voltage domain is active and ready to use. The implementation and functionality of this voltage monitor may vary from device to device, always refer to "Multi-Voltage I/O" chapter of the appropriate device data sheet for more information.