PIC16C774T-I/SO View Datasheet(PDF) - Microchip Technology

Part Name

Description

Manufacturer

PIC16C774T-I/SO

28/40-Pin, 8-Bit CMOS Microcontrollers w/ 12-Bit A/D

Microchip Technology 

PIC16C77X

11.4 Selecting the A/D Conversion Clock

The A/D conversion cycle requires 13TAD: 1 TAD for set-

tling time, and 12 TAD for conversion. The source of the

A/D conversion clock is software selected. The four

possible options for TAD are:

• 2 TOSC

• 8 TOSC

• 32 TOSC

• Internal RC oscillator

Note that these options are the same as those of the

8-bit A/D.

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 11-1 shows the resultant TAD times

derived from the device operating frequencies and the

A/D clock source selected.

The ADIF bit is set on the rising edge of the 14th TAD.

The GO/DONE bit is cleared on the falling edge of the

14th TAD.

TABLE 11-1 TAD vs. DEVICE OPERATING FREQUENCIES

AD Clock Source (TAD)

Device Frequency

Operation

ADCS<1:0>

20 MHz

5 MHz

4 MHz

1.25 MHz

2 TOSC

8 TOSC

32 TOSC

RC

00

100 ns(2)

400 ns(2)

500 ns(2)

1.6 s

01

800 ns(2)

1.6 s

2.0 s

6.4 s

10

1.6 s

6.4 s

8.0 s(3)

24 s(3)

11

2 - 6 s(1,4)

2 - 6 s(1,4)

2 - 6 s(1,4)

2 - 6 s(1,4)

Note 1: The 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 RC A/D conversion clock source is only recommended if the conver-

sion will be performed during sleep.

11.5 A/D Conversions

Figure 11-5 shows an example that performs an A/D

conversion. The port pins are configured as analog

inputs. The analog reference VREF+ is the device AVDD

and the analog reference VREF- is the device AVSS. The

A/D interrupt is enabled, and the A/D conversion clock

is TRC. The conversion is performed on the AN0 chan-

nel.

FIGURE 11-4: PERFORMING AN A/D CONVERSION

BCF

PIR1, ADIF

;Clear A/D Int Flag

BSF

STATUS, RP0 ;Select Page 1

CLRF ADCON1

;Configure A/D Inputs

BSF

PIE1, ADIE

;Enable A/D interrupt

BCF

STATUS, RP0 ;Select Page 0

MOVLW 0xC1

;RC clock, A/D is on,

;Ch 0 is selected

MOVWF ADCON0

;

BSF

INTCON, PEIE ;Enable Peripheral

BSF

INTCON, GIE ;Enable All Interrupts

;

; Ensure that the required sampling time for the

; selected input channel has lapsed. Then the

; conversion may be started.

BSF

ADCON0, GO

;Start A/D Conversion

:

;The ADIF bit will be

;set and the GO/DONE bit

:

;cleared upon completion-

;of the A/D conversion.

 1999-2013 Microchip Technology Inc.

Advance Information

DS30275B-page 121

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