DM163006 datasheet(200/320 Pages) MICROCHIP

200 / 320 page

PIC18C601/801

DS39541A-page 200

Advance Information

 2001 Microchip Technology Inc.

17.4

A/D Conversions

Figure 17-3 shows the operation of the A/D converter

after the GO bit has been set. Clearing the GO/DONE

bit during a conversion will abort the current conver-

sion. The A/D result register pair will NOT be updated

with the partially completed A/D conversion sample.

That is, the ADRESH:ADRESL registers will continue

to contain the value of the last completed conversion

(or the last value written to the ADRESH:ADRESL reg-

isters). After the A/D conversion is aborted, a 2TAD wait

is required before the next acquisition is started. After

this 2TAD wait, acquisition on the selected channel is

automatically started.

17.5

Use of the CCP2 Trigger

An A/D conversion can be started by the “special event

trigger” of the CCP2 module. This requires that the

CCP2M3:CCP2M0

bits

(CCP2CON<3:0>)

pro-

grammed as 1011, and that the A/D module is enabled

(ADON bit is set). When the trigger occurs, the GO/DONE

bit will be set, starting the A/D conversion and the Timer1

(or Timer3) counter will be reset to zero. Timer1 (or

Timer3) is reset to automatically repeat the A/D acquisi-

tion period with minimal software overhead (moving

ADRESH/ADRESL to the desired location). The appropri-

ate analog input channel must be selected and the mini-

mum acquisition done before the “special event trigger”

sets the GO/DONE bit (starts a conversion).

If the A/D module is not enabled (ADON is cleared), the

“special event trigger” will be ignored by the A/D mod-

ule, but will still reset the Timer1 (or Timer3) counter.

FIGURE 17-3:

A/D CONVERSION TAD CYCLES

Note:

The GO/DONE bit should NOT be set in

the same instruction that turns on the A/D.

TAD1 TAD2 TAD3 TAD4 TAD5 TAD6 TAD7 TAD8

TAD11

Set GO bit

Holding capacitor is disconnected from analog input (typically 100 ns)

TAD9 TAD10

TCY - TAD

Next Q4: ADRESH/ADRESL is loaded, GO bit is cleared,

ADIF bit is set, holding capacitor is connected to analog input.

Conversion Starts

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