PIC16LC715-20I/SO View Datasheet(PDF) - Microchip Technology

Part Name

Description

Manufacturer

PIC16LC715-20I/SO

8-Bit CMOS Microcontrollers with A/D Converter

Microchip Technology 

PIC16C71X

7.2 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:

2.0 µs for the PIC16C71

1.6 µs for all other PIC16C71X devices

Table 7-1 and Table 7-2 and show the resultant TAD

times derived from the device operating frequencies

and the A/D clock source selected.

7.3 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 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 AN7:AN0

pins), may cause the input buffer to con-

sume current that is out of the devices

specification.

TABLE 7-1: TAD vs. DEVICE OPERATING FREQUENCIES, PIC16C71

AD Clock Source (TAD)

Device Frequency

Operation ADCS1:ADCS0

20 MHz

16 MHz

4 MHz

1 MHz

333.33 kHz

2TOSC

00

100 ns(2)

125 ns(2)

500 ns(2)

2.0 µs

6 µs

8TOSC

01

400 ns(2)

500 ns(2)

2.0 µs

8.0 µs

24 µs(3)

32TOSC

10

1.6 µs(2)

2.0 µs

8.0 µs

32.0 µs(3)

96 µs(3)

RC(5)

11

2 - 6 µs(1,4)

2 - 6 µs(1,4)

2 - 6 µs(1,4)

2 - 6 µs(1)

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 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.

TABLE 7-2: TAD vs. DEVICE OPERATING FREQUENCIES, PIC16C710/711, PIC16C715

AD Clock Source (TAD)

Device Frequency

Operation

ADCS1:ADCS0

20 MHz

5 MHz

1.25 MHz

333.33 kHz

2TOSC

00

100 ns(2)

400 ns(2)

1.6 µs

6 µs

8TOSC

01

400 ns(2)

1.6 µs

6.4 µs

24 µs(3)

32TOSC

10

1.6 µs

6.4 µs

25.6 µs(3)

96 µs(3)

RC(5)

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 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.

© 1997 Microchip Technology Inc.

DS30272A-page 41

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