Vault 7: Projects
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PIC24F Family Reference Manual
DS39741A-page 48-22 Preliminary © 2010 Microchip Technology Inc.
Table 48-1: Typical Voltage Reference with CVRSRC = 3.3V
48.6.1 Configuring the Comparator Voltage Reference
The voltage range selected by the CVRR bit (CVRCON<5>) determines the size of the steps
selected by the CVR<3:0> bits (CVRCON<3:0>). One range (CVRR = 0) provides finer
resolution by offering smaller voltage increments for each step. The equations used to calculate
the comparator voltage reference are as follows:
If CVRR =
1:
Voltage Reference = ((CVR<3:0>)/24) * (CVRSRC)
If CVRR =
0:
Voltage Reference = (CVRSRC/4) + ((CVR<3:0>)/32) * (CVRSRC)
48.6.2 Voltage Reference Accuracy/Error
The full voltage reference range cannot be realized because the transistors on the top and
bottom of the resistor ladder network, as shown in Figure 48-7, keep the voltage reference from
approaching the reference source rails. The voltage reference is derived from the reference
source; therefore, the voltage reference output changes with fluctuations in the reference source.
For reference voltage accuracy, refer to the “Electrical Characteristics” chapter of the specific
device data sheet.
48.6.3 Operation During Sleep Mode
When the device wakes up from Sleep mode through an interrupt or a Watchdog Timer time-out,
the contents of the CVRCON register are not affected. To minimize current consumption in Sleep
mode, the voltage reference should be disabled.
48.6.4 Effects of a Reset
A device Reset has the following effects:
• Disables the voltage reference by clearing the CVREN bit (CVRCON<7>)
• Disconnects the reference from the CV
REF pin by clearing the CVROE bit (CVRCON<6>)
• Selects the high-voltage range by clearing the CVRR bit (CVRCON<5>)
• Clears the CVR value bits (CVRCON<3:0>)
CVR<3:0> Tap
Voltage Reference
CVRR = 0 CVRR = 1
0000 0 0.83V 0.00V
0001 1 0.93V 0.14V
0010 2 1.03V 0.28V
0011 3 1.13V 0.41V
0100 4 1.24V 0.55V
0101 5 1.34V 0.69V
0110 6 1.44V 0.83V
0111 7 1.55V 0.96V
1000 8 1.65V 1.10V
1001 9 1.75V 1.24V
1010 10 1.86V 1.38V
1011 11 1.96V 1.51V
1100 12 2.06V 1.65V
1101 13 2.17V 1.79V
1110 14 2.27V 1.93V
1111 15 2.37V 2.06V
Protego_Release_01_05-Related-OEM-Documentation-PIC24FJ32MC10X-Reference_Manual-Section48-Comparator_with_Blanking.pdf