PIC16C923T-08I/SP View Datasheet(PDF) - Microchip Technology
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PIC16C923T-08I/SP Datasheet PDF : 189 Pages
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12.2 Selecting the A/D Conversion Clock
The A/D conversion time per bit is defined as TAD. The
A/D conversion requires 9.5 TAD per 8-bit conversion.
The source of the A/D conversion clock is software
selected. The four possible options for TAD are:
• 2TOSC
• 8TOSC
• 32TOSC
• 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 12-1 shows the resultant TAD times derived from
the device operating frequencies and the A/D clock
source selected.
PIC16C9XX
12.3 Configuring Analog Port Pins
The ADCON1 and TRISA 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 (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
configured as analog inputs 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 accu-
racy.
Note 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 devices
specification.
TABLE 12-1: TAD vs. DEVICE OPERATING FREQUENCIES
A/D Clock Source (TAD)
Device Frequency
Operation
ADCS1:ADCS0
8 MHz
5 MHz
1.25 MHz
333.33 kHz
2TOSC
00
250 ns(2)
400 ns(2)
1.6 µs
6 µs
8TOSC
01
1 µs
1.6 µs
6.4 µs
24 µs(3)
32TOSC
10
4 µs
6.4 µs
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 TAD time.
3: For faster conversion times, the selection of another clock source is recommended.
4: When derived frequency is greater than 1 MHz, the RC A/D conversion clock source is recommended for
sleep mode only
5: For extended voltage devices (LC), please refer to the electrical specifications section.
© 1997 Microchip Technology Inc.
DS30444E - page 83
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