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DM74LS47 数据表(PDF) 2 Page - Fairchild Semiconductor |
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DM74LS47 数据表(HTML) 2 Page - Fairchild Semiconductor |
2 / 6 page www.fairchildsemi.com 2 Truth Table Note 2: BI/RBO is wire-AND logic serving as blanking input (BI) and/or ripple-blanking output (RBO). The blanking out (BI) must be open or held at a HIGH level when output functions 0 through 15 are desired, and ripple-blanking input (RBI) must be open or at a HIGH level if blanking or a decimal 0 is not desired. X = input may be HIGH or LOW. Note 3: When a LOW level is applied to the blanking input (forced condition) all segment outputs go to a HIGH level regardless of the state of any other input condition. Note 4: When ripple-blanking input (RBI) and inputs A0, A1, A2 and A3 are LOW level, with the lamp test input at HIGH level, all segment outputs go to a HIGH level and the ripple-blanking output (RBO) goes to a LOW level (response condition). Note 5: When the blanking input/ripple-blanking output (BI/RBO) is OPEN or held at a HIGH level, and a LOW level is applied to lamp test input, all segment outputs go to a LOW level. Functional Description The DM74LS47 decodes the input data in the pattern indi- cated in the Truth Table and the segment identification illustration. If the input data is decimal zero, a LOW signal applied to the RBI blanks the display and causes a multi- digit display. For example, by grounding the RBI of the highest order decoder and connecting its BI/RBO to RBI of the next lowest order decoder, etc., leading zeros will be suppressed. Similarly, by grounding RBI of the lowest order decoder and connecting its BI/RBO to RBI of the next high- est order decoder, etc., trailing zeros will be suppressed. Leading and trailing zeros can be suppressed simulta- neously by using external gates, i.e.: by driving RBI of a intermediate decoder from an OR gate whose inputs are BI/RBO of the next highest and lowest order decoders. BI/ RBO also serves as an unconditional blanking input. The internal NAND gate that generates the RBO signal has a resistive pull-up, as opposed to a totem pole, and thus BI/ RBO can be forced LOW by external means, using wired- collector logic. A LOW signal thus applied to BI/RBO turns off all segment outputs. This blanking feature can be used to control display intensity by varying the duty cycle of the blanking signal. A LOW signal applied to LT turns on all segment outputs, provided that BI/RBO is not forced LOW. Decimal Inputs Outputs or Note Function LT RBI A3 A2 A1 A0 BI/RBO a b c d e f g 0 H H L L L L H L LLL LL H (Note 2) 1 H X L L L H H H L L H H H H (Note 2) 2H X L L H L H L L H L L H L 3 H X L L H HHL L L L H H L 4H X L H L L H H L L H H L L 5 H X L H L HHL H L L H L L 6 H X L H H L H H H LL LLL 7 H X L H H HHL L L H H H H 8 H X H L L L H L LLL LLL 9 H X H L L H H L LL H H LL 10 H X H L H L H H H H L L H L 11 H X H L H H H H HL L H HL 12 H X H H L L H H L H H H L L 13 H X H H L HHL H H L H L L 14 H X HHH L H H H H L L L L 15 H X H H H H H H HHH HHH BI XXX XXX L H H H H H H H (Note 3) RBI H L L L L L L H HHH HHH (Note 4) LT L X X X X X H L LLL LLL (Note 5) |
类似零件编号 - DM74LS47 |
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类似说明 - DM74LS47 |
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