TC820CKW View Datasheet(PDF) - Microchip Technology
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TC820CKW Datasheet PDF : 28 Pages
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4.0 FUNCTION CONTROL INPUTS
PIN
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
Logic Input
FREQ/
VOLTS
RANGE/
FREQ
LOGIC
TC820 Function
X
X
1 Logic Probe
0
0
0 A/D Converter,
VFULL SCALE = 2 x VREF
0
1
0 A/D Converter,
VFULL SCALE = 20 x VREF
1 Frequency 0 Frequency Counter
Counter
Input
Note 1: Logic "0" = DGND
2: 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 5µA 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 5µA 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-
nected to VDD, 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 – 1.5V and
DGND +1.5V), an external buffer is recommended.
© 2002 Microchip Technology Inc.
TC820
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 5µA pull-downs
to DGND when the Voltage/Frequency Measurement
mode is active.
TABLE 4-2:
DP1
0
0
1
1
TC820 DECIMAL POINT
TRUTH TABLE
DP0
LCD
0
3999
1
399.9
0
39.99
1
3.999
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-
nected to VDD, 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.
DS21476B-page 15
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