DM163006 Datasheet, PDF (199/320 Pages) Microchip Technology – High-Performance ROM-less Microcontrollers

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. There are seven possible options for TAD:
• 2TOSC
• 4TOSC
• 8TOSC
• 16TOSC
• 32TOSC
• 64TOSC
• Internal RC oscillator
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.
PIC18C601/801
17.3 Configuring Analog Port Pins
The ADCON1, TRISA, TRISF and TRISH registers
control the operation of the A/D port pins. The port pins
needed as analog inputs must have their correspond-
ing TRIS bits set (input). If the TRIS bit is cleared (out-
put), the digital output level (VOH or VOL) will be
converted.
The A/D operation is independent of the state of the
CHS3:CHS0 bits and the TRIS bits.
Note 1: When reading the port register, all pins
configured as analog input channels will
read as cleared (a low level). Pins config-
ured as digital inputs will convert an ana-
log input. Analog levels on a digitally
configured input will not affect the conver-
sion accuracy.
2: Analog levels on any pin defined as a dig-
ital input may cause the input buffer to
consume current out of the device’s spec-
ification limits.
TABLE 17-1: TAD vs. DEVICE OPERATING FREQUENCIES
AD Clock Source (TAD)
Maximum Device Frequency
Operation
ADCS2:ADCS0
PIC18C601/801
PIC18LC601/801⁽⁵⁾
2TOSC
000
1.25 MHz
666 kHz
4TOSC
100
2.50 MHz
1.33 MHz
8TOSC
001
5.00 MHz
2.67 MHz
16TOSC
101
10.0 MHz
5.33 MHz
32TOSC
010
20.0 MHz
10.67 MHz
64TOSC
110
—
—
RC
x11
—
—
Note 1: The RC source has a typical TAD time of 4 µs.
2: These values violate the minimum required TAD time.
3: For faster conversion times, the selection of another clock source is recommended.
4: For device frequencies above 1 MHz, the device must be in SLEEP for the entire conversion or the A/D
accuracy may be out of specification.
5: This column is for the LC devices only.
 2001 Microchip Technology Inc.
Advance Information
DS39541A-page 199