12F629 datasheet(44/136 Pages) MICROCHIP

44 / 136 page

PIC12F629/675

DS41190G-page 44

 2010 Microchip Technology Inc.

TABLE 7-1:

TAD vs. DEVICE OPERATING FREQUENCIES

7.1.5

STARTING A CONVERSION

The A/D conversion is initiated by setting the

GO/DONE bit (ADCON0<1>). When the conversion is

complete, the A/D module:

• Clears the GO/DONE bit

• Sets the ADIF flag (PIR1<6>)

• Generates an interrupt (if enabled)

If the conversion must be aborted, the GO/DONE bit

can be cleared in software. The ADRESH:ADRESL

registers will not be updated with the partially complete

A/D

conversion

sample.

Instead,

the

ADRESH:ADRESL registers will retain the value of the

previous conversion. After an aborted conversion, a

2TAD delay is required before another acquisition can

be initiated. Following the delay, an input acquisition is

automatically started on the selected channel.

7.1.6

CONVERSION OUTPUT

The A/D conversion can be supplied in two formats: left

or right shifted. The ADFM bit (ADCON0<7>) controls

the output format. Figure 7-2 shows the output formats.

FIGURE 7-2:

10-BIT A/D RESULT FORMAT

A/D Clock Source (TAD)

Device Frequency

Operation

ADCS2:ADCS0

20 MHz

5 MHz

4 MHz

1.25 MHz

2 TOSC

000

100 ns(2)

400 ns(2)

500 ns(2)

1.6

s

4 TOSC

100

200 ns(2)

800 ns(2)

1.0

s(2)

3.2

s

8 TOSC

001

400 ns(2)

1.6

s2.0 s6.4 s

16 TOSC

101

800 ns(2)

3.2

s4.0 s

12.8

s(3)

32 TOSC

010

1.6

s6.4 s

8.0

s(3)

25.6

s(3)

64 TOSC

110

3.2

s

12.8

s(3)

16.0

s(3)

51.2

s(3)

A/D RC

x11

2 - 6

s(1,4)

2 - 6

s(1,4)

2 - 6

s(1,4)

2 - 6

s(1,4)

Legend: Shaded cells are outside of recommended range.

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

s for VDD > 3.0V.

2: These values violate the minimum required TAD time.

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

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

conversion will be performed during Sleep.

Note:

The GO/DONE bit should not be set in the

same instruction that turns on the A/D.

ADRESH

ADRESL

(ADFM =

0)MSB

LSB

Bit 7

Bit 0

Bit 7

Bit 0

10-bit A/D Result

Unimplemented: Read as ‘

0’

(ADFM =

MSB

LSB

Bit 7

Bit 0

Bit 7

Bit 0

Unimplemented: Read as ‘

0’

10-bit A/D Result

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