TC818 datasheet(11/24 Pages) MICROCHIP

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DS21475B-page 11

TC818A

FIGURE 3-4:

BASIC TC818A CONVERSION TIMING

3.9

Manual Range Selection

The TC818A voltage and resistance auto-ranging fea-

ture can be disabled by momentarily bringing RANGE

(Pin 59) to digital ground potential (Pin 58). When the

change from auto-to-manual ranging occurs, the first

manual range selected is the last range in the Auto-

Ranging mode.

The TC818A power-up circuit initially selects auto-

range operation. Once the manual range option is

entered, range changes are made by momentarily

grounding the RANGE control input. The TC818A

remains in the Manual Range mode until the measure-

ment function (voltage or resistance), or measurement

option (AC/DC,

Ω/LOΩ) changes. This causes the

TC818A to return to auto-ranging operation.

The “Auto” LCD annunciator driver is active only in the

Auto-Range mode.

Figure 3-5 shows typical operation where the manual

range selection option is used. Also shown is the

extended resolution display format. Also, see Figure 3-6

and Figure 3-7.

FIGURE 3-5:

MANUAL RANGE

SELECTION RESISTANCE

MEASUREMENTS

TC818A

Signal

INT

Phase

REF

DEINT

Phase

Auto-Zero

Phase

Min. Auto-Zero

Time

Fixed

1638.5tP

Next Conversion

Auto-Zero Cycle

Extended Resolution

Zero Crossing

*In Auto-Range Operation, Maximum

is 2000tP and minimum Auto-Zero Time is 4361.5tP

3361.5tP

*Max.

3000tP

tCONV = 8000tP

tDE

Input

Signal

External Crystal = 32.768kHz

Internal Clock Period = tP = 2/32.768 = 61.04µsec

Total Conversion Time = tCONV = 8000(tP)

= 488.3msec

≈ 2 conv/sec

Integration Time = TI = 1638.5(tP) = 100msec

Maximum Reference De-integrate Time

= tDE 3000(tP) = 183.1msec

(manual extended resolution)

= 2000(tP) = 122.1msec (auto-range)

Maximum Auto-Zero Time

= (8000 - 3000 - 1638.5)

(tP) = 205.1msec (manual extended resolution)

= (8000 - 3000 - 1638.5)

(tP) = 205.1msec (manual extended resolution)

RX < 19

RX > 3000

RX > 2000

Continuity

Indicator

Continuous

4kHz Buzzer

Yes

Extended Resolution

Feature

Yes*

Display

True

Reading

*Mode also operates when Auto-Ranging Operator is selected

and 2M

Ω < RX < 2.999MΩ.

Yes

Display

"1" 000

Display Last

3 Digits and

Flash MSD

Over Range

Indicator

"1" = > Flashing

MSD

Manual

Range

Select

Output 4kHz

Audio

Frequency

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