PIC16C72 datasheet(57/128 Pages) MICROCHIP

57 / 128 page

PIC16C72 Series

 1998-2013 Microchip Technology Inc.

Preliminary

DS39016B-page 57

9.2

Selecting the A/D Conversion Clock

The A/D conversion time per bit is defined as TAD. The

A/D conversion requires 9.5TAD per 8-bit conversion.

The source of the A/D conversion clock is software

selectable. 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

s.

Table 9-1 shows the resultant TAD times derived from

the device operating frequencies and the A/D clock

source selected.

9.3

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.

TABLE 9-1

TAD vs. DEVICE OPERATING FREQUENCIES

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.

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.

AD Clock Source (TAD)

Device Frequency

Operation

ADCS1:ADCS0

20 MHz

5 MHz

1.25 MHz

333.33 kHz

2TOSC

100 ns(2)

400 ns(2)

1.6

s6 s

8TOSC

400 ns(2)

1.6

s6.4 s

s(3)

32TOSC

1.6

s6.4 s

25.6

s(3)

RC(5)

2 - 6

s(1,4)

2 - 6

s(1,4)

2 - 6

s(1,4)

2 - 6

s(1)

Legend: Shaded cells are outside of recommended range.

Note 1: The RC source has a typical TAD time of 4

s.

2: These values violate the minimum required TAD time.

3: For faster conversion times, the selection of another clock source is recommended.

4: When device frequency is greater than 1 MHz, the RC A/D conversion clock source is recommended for

sleep operation only.

5: For extended voltage devices (LC), please refer to Electrical Specifications section.

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