The Voltage Reference (VREF) is a device that produces a fixed (constant) voltage, providing references to the analog comparators and external circuitry. The voltages include /3 and /4 dividers of the VDD power supply as well as external sources. The macrocell also has an option to output reference voltages on PIN 18 and 19.
The Vref output pin will slave its output from the input to the selected analog block. The output reference can be changed from the sources’ properties window.
• PIN18: is only for VREF1;
• PIN19: is only for VREF0;
Table 1.
| VDD | Practical VREF range | Note |
|---|---|---|
| 2.0V-5.5V | 50mV ~1.2V | |
| 1.7V – 2.0V | 50mV ~1.1V | Higher than 1.1V negative input, the comparator may show wrong result |