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ICL7129CPL Datasheet(PDF) 7 Page - Intersil Corporation |
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ICL7129CPL Datasheet(HTML) 7 Page - Intersil Corporation |
7 / 11 page 3-37 (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. 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 VDISP to V+ and is in sync with the three back- 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. + - BUFFER 500k Ω IN HI COMMON IN LO V 200mV + - + - CONTINUITY TO DISPLAY DRIVER (NOT LATCHED) FIGURE 7. “INSTANT CONTINUITY” COMPARATOR AND OUTPUT STRUCTURE a b c d f g e a b c d f g e B1, C1, CONTINUITY BACKPLANE CONNECTIONS BP1 BP2 BP3 A1, G1, D1 F1, E1, DP1 B2, C2, LOW BATTERY A2, G2, D2 F2, E2, DP2 F4, E4, DP4 A4, G4, D4 B4, C4, BC5 F3, E3, DP3 A3, G3, D3 B3, C3, MINUS f e a b c d f g e a b c d f g e LOW BATTERY CONTINUITY c a b c d f g e a b c d f g e f e a b c d f g e a b c d f g e LOW BATTERY CONTINUITY c FIGURE 8. TRIPLEXED LIQUID CRYSTAL DISPLAY LAYOUT FOR ICL7129 ICL7129 |
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