ICL7129 Intersil, ICL7129 Datasheet - Page 7

• Manufacturer Part Number: ICL7129
• Description: 41/2 Digit LCD/ Single-Chip A/D Converter
• Manufacturer: Intersil

(UR pin 21) outputs are latched on the falling edge of
LATCH/HOLD and remain in that state until the end of the
next conversion cycle. In addition, digits 1 through 4 are
blanked during overrange. All three of these pins are “weak
outputs” and can be overridden with external drivers or pull-
up resistors to enable their input functions as described in
the Pin Description table.
Instant Continuity
A comparator with a built-in 200mV offset is connected
directly between INPUT HI and INPUT LO of the ICL7129
(Figure 7). The CONTINUITY output (pin 27) will be pulled
high whenever the voltage between the analog inputs is less
than 200mV. This will also turn on the “CONTINUITY”
annunciator on the display. The CONTINUITY output may be
used to enable an external alarm or buzzer, thereby giving
the ICL7129 an audible continuity checking capability.
CONTINUITY
FIGURE 7. “INSTANT CONTINUITY” COMPARATOR AND
COMMON
IN LO
IN HI
B3, C3, MINUS
OUTPUT STRUCTURE
B4, C4, BC5
F4, E4, DP4
F3, E3, DP3
A4, G4, D4
A3, G3, D3
200mV
-
V
+
-
+
FIGURE 8. TRIPLEXED LIQUID CRYSTAL DISPLAY LAYOUT FOR ICL7129
c
c
500k
e
e
f
f
e
e
f
f
d
d
LOW BATTERY CONTINUITY
LOW BATTERY CONTINUITY
g
g
a
a
c
c
b
b
+
-
BUFFER
TO DISPLAY
DRIVER
(NOT LATCHED)
e
e
f
f
d
d
g
g
a
a
c
c
b
b
ICL7129
3-37
e
e
f
f
Since the CONTINUITY output is one of the four “weak out-
puts” of the ICL7129, the “continuity” annunciator on the dis-
play can be driven by an external source if desired. The
continuity function can be overridden with a pull-down resistor
connected between CONTINUITY pin and DGND (pin 36).
Display Configuration
The ICL7129 is designed to drive a triplexed liquid crystal
display. This type of display has three backplanes and is driven
in a multiplexed format similar to the ICM7231 display driver
family. The specific display format is shown in Figure 8. Notice
that the polarity sign, decimal points, “LOW BATTERY”, and
“CONTINUITY” annunciators are directly driven by the
ICL7129. The individual segments and annunciators are
addressed in a manner similar to row-column addressing. Each
backplane (row) is connected to one-third of the total number of
segments. BP1 has all F, A, and B segments of the four least
significant digits. BP2 has all of the C, E, and G segments. BP3
has all D segments, decimal points, and annunciators. The seg-
ment lines (columns) are connected in groups of three bringing
all segments of the display out on just 12 lines.
Annunciator Drive
A special display driver output is provided on the ICL7129
which is intended to drive various kinds of annunciators on
custom multiplexed liquid crystal displays. The ANNUNClATOR
DRIVE output (pin 3) is a squarewave signal running at the
backplane frequency, approximately 100Hz. This signal
swings from V
plane outputs BP1, BP2, and BP3. Figure 9 shows these
four outputs on the same time and voltage scales.
Any annunciator associated with any of the three backplanes
can be turned on simply by connecting it to the ANNUNClA-
TOR DRIVE pin. To turn an annunciator off connect if to its
backplane. An example of a display and annunciator drive
scheme is shown in Figure 10.
d
d
g
g
a
a
c
c
b
b
e
e
f
f
d
d
g
g
a
a
DISP
c
c
b
b
to V+ and is in sync with the three back-
BP1
BP2
BP3
BACKPLANE
CONNECTIONS
B1, C1, CONTINUITY
A1, G1, D1
F1, E1, DP1
B2, C2, LOW BATTERY
A2, G2, D2
F2, E2, DP2