Datasheet
1997-2013 Microchip Technology Inc. DS30561C-page 49
PIC12C67X
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
selected. The four possible options for TAD are:
•2T
OSC
•8TOSC
•32TOSC
• Internal ADC 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. If the minimum T
AD time of 1.6 s can not be
obtained, T
AD should be 8 s for preferred operation.
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 TRIS Registers control the opera-
tion 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 (V
OH or VOL) will be converted.
The A/D operation is independent of the state of the
CHS<2:0> bits and the TRIS bits.
Note 1: When reading the port register, all pins
configured as analog input channel 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 that is defined as
a digital input (including the AN<3:0>
pins) may cause the input buffer to con-
sume current that is out of the devices
specification.
TABLE 8-1: TAD vs. DEVICE OPERATING FREQUENCIES
AD Clock Source (TAD)
Device Frequency
Operation ADCS<1:0> 4 MHz 1.25 MHz 333.33 kHz
2T
OSC 00
500 ns
(2)
1.6 s6 s
8T
OSC 01 2.0 s6.4 s
24 s
(3)
32TOSC 10 8.0 s
25.6 s
(3)
96 s
(3)
Internal ADC RC Oscillator
(5)
11
2 - 6 s
(1,4)
2 - 6 s
(1,4)
2 - 6 s
(1)
Note 1: The RC source has a typical TAD time of 4 s.
2: These values violate the minimum required T
AD time.
3: For faster conversion times, the selection of another clock source is recommended.
4: While in RC mode, with device frequency above 1 MHz, conversion accuracy is out of specification.
5: For extended voltage devices (LC), please refer to Electrical Specifications section.