PIC18LF252-ISP Datasheet, PDF (188/332 Pages) Microchip Technology – High-Performance, Enhanced Flash Microcontrollers with 10-Bit A/D

PIC18FXX2
17.2 Selecting the A/D Conversion Clock
The A/D conversion time per bit is defined as TAD. The
A/D conversion requires 12 TAD per 10-bit conversion.
The source of the A/D conversion clock is software
selectable. The seven possible options for TAD are:
• 2 TOSC
• 4 TOSC
• 8 TOSC
• 16 TOSC
• 32 TOSC
• 64 TOSC
• Internal A/D module RC oscillator (2-6 μs)
For correct A/D conversions, the A/D conversion clock
(TAD) must be selected to ensure a minimum TAD time
of 1.6 μs.
Table 17-1 shows the resultant TAD times derived from
the device operating frequencies and the A/D clock
source selected.
17.3 Configuring Analog Port Pins
The ADCON1, TRISA and TRISE registers control the
operation of the A/D port pins. The port pins that are
desired as analog inputs, must have their corresponding
TRIS bits set (input). If the TRIS bit is cleared (output),
the digital output level (VOH or VOL) will be converted.
The A/D operation is independent of the state of the
CHS2:CHS0 bits and the TRIS bits.
Note 1: When reading the port register, all pins con-
figured 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 AN4:AN0
pins) may cause the input buffer to con-
sume current that is out of the device’s
specification.
TABLE 17-1: TAD vs. DEVICE OPERATING FREQUENCIES
AD Clock Source (TAD)
Operation
ADCS2:ADCS0
2 TOSC
000
4 TOSC
100
8 TOSC
001
16 TOSC
101
32 TOSC
010
64 TOSC
110
RC
011
Maximum Device Frequency
PIC18FXX2
1.25 MHz
2.50 MHz
5.00 MHz
10.00 MHz
20.00 MHz
40.00 MHz
—
PIC18LFXX2
666 kHz
1.33 MHz
2.67 MHz
5.33 MHz
10.67 MHz
21.33 MHz
—
DS39564C-page 186
© 2006 Microchip Technology Inc.