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I am looking at the datasheet for the 74HC4511 (available here), and I am confused by the usage of two of the pins: Firstly, the "Latch Enable" pin (\$\overline{LE}\$), and secondly the "Ripple Blanking" pin (\$\overline{BI}\$).

Looking at the logic table for the IC gives states that if the Latch Enable, is high, and neither of the other two "special pins", \$\overline{BI}\$ and \$\overline{LT}\$ are active, then the output is dependent upon the BCD code applied during the transition of \$\overline{LE}\$ from low to high. Does this mean that it stores the BCD state and continues to output the corresponding 7-segment output (for instance if \$0001\$ was applied whilst \$\overline{LE}\$ was transitioning, and then was subsequently changed to \$0010\$, the 7-segment display would continue to display \$1\$ rather than \$2\$?).

I am more confused by the purpose of the Ripple Blanking input, it appears that this simply blanks the 7-segment display, but I do not know what the purpose of this would be, when you can simply set the BCD code to \$1111\$?)

Thanks in advance, and sorry if this is obvious!

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If the 4-bit data input to one 4511 is being shared with another 4511, LE allows you to set-up the 4-bit data for one device (then store it on internal registers). Then you can set up the appropriate 4-bit data (using the same data lines) for another 4511 and have a separate LE pin to store this different data to the 2nd device.

If you didn't have this feature you would have to use 4 lines dedicated to each driver and that is inefficient.

The blanking input disables all segments.

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  • \$\begingroup\$ Ahh, so you can use the same 4-bit bus for an arbitrary number of 4511 ICs adding a single independent bit for each register? \$\endgroup\$ – Thomas Russell Apr 12 '14 at 9:25
  • \$\begingroup\$ Absolutely correct. \$\endgroup\$ – Andy aka Apr 12 '14 at 9:28
  • \$\begingroup\$ Thank you very much for your answer; although I'm still not convinced of the usefulness of the blanking input (why it is included when setting \$1111\$ has the same result). \$\endgroup\$ – Thomas Russell Apr 12 '14 at 9:38
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    \$\begingroup\$ The use case of a blanking input is used to suppress leading 0's. It would be connected to a circuit that determines whether the digit itself or all lower digits are 0. \$\endgroup\$ – Wouter van Ooijen Apr 12 '14 at 10:21
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    \$\begingroup\$ @Shaktal - if you have a 5 digit display and you want to display the number 23, you don't want to display it as 00023 \$\endgroup\$ – Andy aka Apr 12 '14 at 11:51

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