TC820CPL datasheet(15/28 Pages) MICROCHIP

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DS21476B-page 15

TC820

4.0

FUNCTION CONTROL INPUTS

4.1

Functional Description

The TC820 Operating modes are selected with the

function control inputs. See the control input truth,

Table 4-1. The high logic threshold is

≥ VDD –1.5V and

the low logic level is

≤ DGND +1.5V.

TABLE 4-1:

TC820 CONTROL INPUT

TRUTH TABLE

Note

Logic "0" = DGND

Logic "1" = VDD-

4.1.1

FREQ/VOLTS

This input determines whether the TC820 is in the Ana-

log-to-Digital Conversion mode, or in the Frequency

Counter mode. When FREQ/VOLTS is connected to

VDD, the TC820 will measure frequency at the RANGE/

FREQ input. When unconnected, or connected to

DGND, the TC820 will operate as an analog-to-digital

converter. This input has an internal 5

µA pull-down to

DGND.

4.1.2

LOGIC

The LOGIC input is used to activate the logic probe

function. When connected to VDD, the TC820 will enter

the Logic Probe mode. The LCD will show "OL" and all

decimal points will be off. The decimal point inputs

directly control "high" and "low" display annunciators.

When LOGIC is unconnected, or connected to DGND,

the TC820 will perform analog-to-digital or frequency

measurements, as selected by the FREQ/VOLTS

input. The LOGIC input has an internal 5

µA pull-down

to DGND.

4.1.3

RANGE/FREQ

The function of this dual purpose pin is determined by

the FREQ/VOLTS input. When FREQ/VOLTS is con-

nectedtoVDD, RANGE/FREQ is the input for the fre-

quency counter function. Pulses at this input are

counted with a time-base equal to FOSC/40,000. Since

this input has CMOS input levels (VDD –1.5Vand

DGND +1.5V), an external buffer is recommended.

When the TC820 analog-to-digital converter function is

selected, connecting RANGE/FREQ to VDD will divide

the integration time by 10. Therefore, the RANGE/

FREQ input can be used to perform a 10:1 range

change without changing external components.

4.1.4

DP0/LO, DP1/HI

The function of these dual purpose pins is determined

by the LOGIC input. When the TC820 is in the Analog-

to-Digital Converter mode, these inputs control the

LCD decimal points. See the decimal point truth,

Table 4-2. These inputs have internal 5

µA pull-downs

to DGND when the Voltage/Frequency Measurement

mode is active.

Connecting the LOGIC input to VDD places the TC820

in the Logic Probe mode. In this mode, the DP0/LO and

DP1/HI inputs control the LCD "low" and "high" annun-

ciators directly. When DP1/HI is connected to VDD,the

"high" annunciator will turn on. When DP0/LO is con-

nectedtoVDD, the "low" annunciator and the buzzer

will turn on. The internal pull-downs on these pins are

disabled when the logic probe function is selected.

These inputs have CMOS logic switching thresholds.

For optimum performance as a logic probe, external

level shifters are recommended. See the applications

section for details.

4.1.5

BUZIN

This input controls the TC820 on-chip buzzer driver.

Connecting BUZIN to VDD will turn the buzzer on.

There is an external pull-down to DGND. BUZIN can be

used with external circuitry to provide additional func-

tions, such as a fast, audible continuity indication.

4.2

Additional Features

The TC820 is available in 40-pin and 44-pin packages.

Several additional features are available in the 44-pin

package.

Logic Input

TC820 Function

FREQ/

VOLTS

RANGE/

FREQ

LOGIC

Logic Probe

A/D Converter,

VFULL SCALE =2x VREF

A/D Converter,

VFULL SCALE =20 x VREF

Frequency

Counter

Input

Frequency Counter

TABLE 4-2:

TC820 DECIMAL POINT

TRUTH TABLE

DP1

DP0

LCD

3999

399.9

39.99

3.999

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