PIC18F2680ISPQTP datasheet(253/482 Pages) MICROCHIP

253 / 482 page

Preliminary

DS39625C-page 251

PIC18F2585/2680/4585/4680

The value in the ADRESH/ADRESL registers is not

modified for a Power-on Reset. The ADRESH/ADRESL

registers will contain unknown data after a Power-on

Reset.

After the A/D module has been configured as desired,

the selected channel must be acquired before the con-

version is started. The analog input channels must

have their corresponding TRIS bits selected as an

input. To determine acquisition time, see Section 19.1

“A/D Acquisition Requirements”. After this acquisi-

tion time has elapsed, the A/D conversion can be

started. An acquisition time can be programmed to

occur between setting the GO/DONE bit and the actual

start of the conversion.

The following steps should be followed to perform an

A/D conversion:

Configure the A/D module:

• Configure analog pins, voltage reference and

digital I/O (ADCON1)

• Select A/D input channel (ADCON0)

• Select A/D acquisition time (ADCON2)

• Select A/D conversion clock (ADCON2)

• Turn on A/D module (ADCON0)

Configure A/D interrupt (if desired):

• Clear ADIF bit

• Set ADIE bit

• Set GIE bit

Wait the required acquisition time (if required).

Start conversion:

• Set GO/DONE bit (ADCON0 register)

Wait for A/D conversion to complete, by either:

• Polling for the GO/DONE bit to be cleared

• Waiting for the A/D interrupt

Read A/D Result registers (ADRESH:ADRESL);

clear bit ADIF, if required.

For next conversion, go to step 1 or step 2, as

required. The A/D conversion time per bit is

defined as TAD. A minimum wait of 2 TAD is

required before next acquisition starts.

FIGURE 19-2:

ANALOG INPUT MODEL

VAIN

CPIN

ANx

5 pF

VDD

VT = 0.6V

ILEAKAGE

RIC

≤ 1k

Sampling

Switch

RSS

CHOLD = 120 pF

VSS

Sampling Switch

56 7 8 9 10 11

Ω)

VDD

± 500 nA

Legend: CPIN

ILEAKAGE

RIC

CHOLD

= input capacitance

= threshold voltage

= leakage current at the pin due to

= interconnect resistance

= sampling switch

= sample/hold capacitance (from DAC)

various junctions

= sampling switch resistance

RSS

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