Datasheet

 1998-2013 Microchip Technology Inc. DS30289C-page 185
PIC17C7XX
16.2 Selecting the A/D Conversion
Clock
The A/D conversion time per bit is defined as TAD. The
A/D conversion requires a minimum 12T
AD per 10-bit
conversion. The source of the A/D conversion clock is
software selected. The four possible options for T
AD
are:
•8T
OSC
•32TOSC
•64TOSC
• 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 s.
Table 16-1 and Table 16-2 show the resultant TAD times
derived from the device operating frequencies and the
A/D clock source selected. These times are for stan-
dard voltage range devices.
TABLE 16-1: TAD vs. DEVICE OPERATING FREQUENCIES (STANDARD DEVICES (C))
TABLE 16-2: T
AD vs. DEVICE OPERATING FREQUENCIES (EXTENDED VOLTAGE DEVICES (LC))
AD Clock Source (TAD)
Max F
OSC
(MHz)
Operation ADCS1:ADCS0
8T
OSC 00
5
32TOSC 01 20
64TOSC 10 33
RC 11 —
Note: When the device frequency is greater than 1 MHz, the RC A/D conversion clock source is only
recommended for SLEEP operation.
AD Clock Source (TAD)
Max F
OSC
(MHz)
Operation ADCS1:ADCS0
8T
OSC 00
2.67
32TOSC 01 10.67
64T
OSC 10 21.33
RC 11 —
Note: When the device frequency is greater than 1 MHz, the RC A/D conversion clock source is only
recommended for SLEEP operation.