Datasheet

PIC16F716
DS41206A-page 52 Preliminary  2003 Microchip Technology Inc.
8.2 Selecting the A/D Conversion
Clock
The A/D conversion time per bit is defined as TAD. The
A/D conversion requires 9.5 T
AD per 8-bit conversion.
The source of the A/D conversion clock is software
selectable. The four possible options for T
AD are:
•2T
OSC
•8TOSC
•32TOSC
• Internal RC oscillator
For correct A/D conversions, the A/D conversion clock
(T
AD) must be selected to ensure a minimum TAD time
of 1.6 µs.
Table 8-1 shows the resultant T
AD times derived from
the device operating frequencies and the A/D clock
source selected.
8.3 Configuring Analog Port Pins
The ADCON1 and TRISA registers control the
operation of the A/D port pins. The port pins that are
desired as analog inputs must have their correspond-
ing TRIS bits set (input). If the TRIS bit is cleared
(output), the digital output level (V
OH or VOL) will be
converted.
The A/D operation is independent of the state of the
CHS2:CHS0 bits and the TRIS bits.
TABLE 8-1: TAD vs. DEVICE OPERATING FREQUENCIES
Note 1: When reading the port register, all pins
configured as analog input channels will
read as cleared (a low level). Pins
configured as digital inputs, will convert
an analog input. Analog levels on a
digitally configured input will not affect the
conversion accuracy.
2: Analog levels on any pin that is defined as
a digital input (including the AN3:AN0
pins), may cause the input buffer to
consume current that is out of the devices
specification.
AD Clock Source (TAD) Device Frequency
Operation ADCS1:ADCS0 20 MHz 5 MHz 1.25 MHz 333.33 kHz
2T
OSC 00 100 ns
(2)
400 ns
(2)
1.6 µs6µs
8TOSC 01 400 ns
(2)
1.6 µs6.4µs 24 µs
(3)
32 TOSC 10 1.6 µs6.4µs 25.6 µs
(3)
96 µs
(3)
RC 11 2-6 µs
(1), (4)
2-6 µs
(1), (4)
2-6 µs
(1), (4)
2-6 µs
(1)
Legend: Shaded cells are outside of recommended range.
Note 1: The RC source has a typical TAD time of 4 µs.
2: These values violate the minimum required T
AD time.
3: For faster conversion times, the selection of another clock source is recommended.
4: When device frequency is greater than 1 MHz, the RC A/D conversion clock source is recommended for
Sleep operation only.