參數(shù)資料
型號: TC820
廠商: TelCom Semiconductor, Inc.
元件分類: 通用總線功能
英文描述: 3-3/4 DIGIT A/D CONVERTER WITH FREQUENCY COUNTER AND LOGIC PROBE
中文描述: 3-3/4數(shù)字A / D轉(zhuǎn)換頻率計數(shù)器和邏輯探針轉(zhuǎn)爐
文件頁數(shù): 15/22頁
文件大小: 275K
代理商: TC820
3-163
TELCOM SEMICONDUCTOR, INC.
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TC820
3-3/4 A/D CONVERTER WITH
FREQUENCY COUNTER
AND LOGIC PROBE
Additional Features
The TC820 is available in 40-pin and 44-pin packages.
Several additional features are available in the 44-pin pack-
age.
EOC/HOLD
EOC/HOLD is a dual-purpose, bidirectional pin. As an
output, this pin goes low for 10 clock cycles at the end of each
conversion. This pulse latches the conversion data into the
display driver section of the TC820.
EOC/HOLD can be used to hold (or "freeze") the dis-
play. Connecting this pin to V
DD
inhibits the display update
process. Conversions will continue, but the display will not
change. EOC/HOLD will hold the display reading for either
analog-to-digital or frequency measurements.
The input/output structure of the EOC/HOLD pin is
shown in Figure 10. The output drive current is only a few
microAmps, so EOC/HOLD can easily be overdriven by an
open-collector logic gate, as well as a FET, bipolar transis-
tor, or mechanical switch. When used as an output, EOC/
HOLD will have a slow rise and fall time due to the limited
output current drive. A CMOS Schmitt trigger buffer is
recommended.
Connecting the LOGIC input to V
DD
places the TC820
in the logic probe mode. In this mode, the DP0/LO and DP1/
HI inputs control the LCD "low" and "high" annunciators
directly. When DP1/HI is connected to V
DD
, the "high"
annunciator will turn on. When DP0/LO is connected to V
DD
,
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.
BUZ IN
This input controls the TC820 on-chip buzzer driver.
Connecting BUZ IN to V
DD
will turn the buzzer on. There is
an external pull-down to DGND. BUZ IN can be used with
external circuitry to provide additional functions, such as a
fast, audible continuity indication.
Figure 10. EOC/HOLD Pin Schematic
4
500 k
EOC/HOLD
DISPLAY
UPDATE
EOC
TC820
Overrange (OR), Underrange (UR)
The OR output will be high when the analog input signal
is greater than full scale (3999 counts). The UR output will
be high when the display reading is 380 counts or less.
The OR and UR outputs can be used to provide an auto-
ranging meter function. By logically ANDing these outputs
with the inverted EOC/HOLD output, a single pulse will be
generated each time an underranged or overranged conver-
sion occurs (Figure 11).
V
DISP
The V
DISP
input sets the peak-to-peak LCD drive volt-
age. In the 40-pin package, V
DISP
is connected internally to
DGND, providing a typical LCD drive voltage of 5V
P-P
. The
44-pin package includes a separate V
DISP
input for applica-
tions requiring a variable or temperature-compensated LCD
drive voltage. See the applications information for sug-
gested circuits.
EOC/HOLD
TC820
UR
OR
74HC132
*
*
*
*
Figure 11. Generating Underrange and Overrange Pulses
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