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3. Lamp Test : When This pin is low The figure 8 appears on the display. Sice figure 8 shows all displays, you cannot test if you have connected everything properly or not.
4. This is both an input as well as an output pin. When you have a series of numbers, and want to suppress the MSB zeros, you can connect the pin 5 of the LSB 7447 to the MSB 7447. And remember to keep the pin 5 of the LSB explicitly high. Leaving it floating caused me problems.
The ripple blanking doesn't have to be simple, either. Depending upon how you deal with the pins and overall circuit configuration, you can have leading-zero blanking, trailing-zero blanking or both. You can force the blanking of any or all digits, so if you have a display where you'd like to indicate an overrange condition, you can force-blank the entire display at a 0.5-second rate using a 555 timer gated into the RBO/BI pins. Or, you can use these same pins with the same gating and the same (or another) timer to change the blanking pulse width at a 100Hz frequency to provide efficient display brightness. If you're really good (and I've been known to be on occasion), you can use a single 7447 with a multiplexed display and still have leading-zero blanking using a single flip-flop to store the RBO data for the next switch of the MUX.
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