PIC16F631/677/685/687/689/690
TABLE 9-1:
ADC CLOCK PERIOD (TAD) VS. DEVICE OPERATING FREQUENCIES (VDD > 3.0V)
ADC Clock Period (TAD)
Device Frequency (FOSC)
ADC Clock Source
ADCS<2:0>
20 MHz
8 MHz
4 MHz
1 MHz
FOSC/2
FOSC/4
FOSC/8
FOSC/16
FOSC/32
FOSC/64
FRC
000
100
001
101
010
110
x11
100 ns(2)
200 ns(2)
400 ns(2)
800 ns(2)
1.6 μs
250 ns(2)
500 ns(2)
1.0 μs(2)
2.0 μs
500 ns(2)
1.0 μs(2)
2.0 μs
2.0 μs
4.0 μs
8.0 μs(3)
16.0 μs(3)
32.0 μs(3)
64.0 μs(3)
2-6 μs(1,4)
4.0 μs
4.0 μs
8.0 μs(3)
16.0 μs(3)
2-6 μs(1,4)
3.2 μs
2-6 μs(1,4)
8.0 μs(3)
2-6 μs(1,4)
Legend: Shaded cells are outside of recommended range.
Note 1: The FRC source has a typical TAD time of 4 μs for VDD > 3.0V.
2: These values violate the minimum required TAD time.
3: For faster conversion times, the selection of another clock source is recommended.
4: When the device frequency is greater than 1 MHz, the FRC clock source is only recommended if the
conversion will be performed during Sleep.
FIGURE 9-2:
ANALOG-TO-DIGITAL CONVERSION TAD CYCLES
TCY to TAD
TAD1 TAD2 TAD3 TAD4 TAD5 TAD6 TAD7 TAD8 TAD9 TAD10 TAD11
b9
b8
b7
b6
b5
b4
b3
b2
b1
b0
Conversion Starts
Holding Capacitor is disconnected from analog input (typically 100 ns)
Set GO/DONE bit
ADRESH and ADRESL registers are loaded,
GO bit is cleared,
ADIF bit is set,
Holding capacitor is connected to analog input
9.1.5
INTERRUPTS
The ADC module allows for the ability to generate an
interrupt upon completion of an Analog-to-Digital
conversion. The ADC interrupt flag is the ADIF bit in the
PIR1 register. The ADC interrupt enable is the ADIE bit
in the PIE1 register. The ADIF bit must be cleared in
software.
Note:
The ADIF bit is set at the completion of
every conversion, regardless of whether
or not the ADC interrupt is enabled.
This interrupt can be generated while the device is
operating or while in Sleep. If the device is in Sleep, the
interrupt will wake-up the device. Upon waking from
Sleep, the next instruction following the SLEEP
instruction is always executed. If the user is attempting
to wake-up from Sleep and resume in-line code
execution, the global interrupt must be disabled. If the
global interrupt is enabled, execution will switch to the
interrupt service routine.
Please see Section 9.1.5 “Interrupts” for more
information.
© 2007 Microchip Technology Inc.
DS41262D-page 109
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