Lab 6 Digital Display Decoder Slide 2 7
Lab 6 : Digital Display Decoder: Slide #2 7 Segment LED display Slide #3 Display Decoder Fundamentals Slide #4 LT Control Input Slide #5 BI Control Input Slide #6 RBI and RBO Slide #7 Ripple Blanking:
Lab 6 : 7 Segment LED display Digital displays come in various packages and arrangements. The 7 Segment LED display (7 seg disp) is one of the most common and has been around for many years. The display is an IC with 7 LED’s. Lighting up combinations of LED’s can display any number. The 7 LED’s are labeled with industry standard identifiers (a, b, … g). The identifiers are used to designate the position of each LED. There are 2 types of display packages. The package shown is called Common Cathode. It lights the LED when a logic 1 is applied to the input segment. The common pin must be connected to ground. Here is how the number 7 is displayed… The other package is called Common Anode. It lights the LED when a logic 0 is applied to the input segment. The common pin must be connected to Vcc. Here is how the number 7 is displayed… a 1 1 0 a 0 f Common Catthode 0 1 0 g e c b 5 V f d Common Anode 1 0 1 g e 1 0 Slide #2 0 1 b d c
Lab 6 : 7 Segment Decoder The 7 Segment LED display package is connected to a decoder. The decoder receives the binary code at inputs D C B A and lights the appropriate segments. This display decoder has active high outputs. It connects to a Common Cathode display. The decoder has 3 Active Low control inputs LT, RBI, BI. They will be disabled for now and explained later. The decoder has an internal logic gate system that takes the 4 bit number applied to D C B A and lights up the LEDs to display that number. Here is an example of the decoder displaying the number 5. The number 5 is applied to the input. D is MSB and A is LSB. The decoder internal logic gate system outputs the binary combination to display 5 at a, b, … g. Logic 1 at an output forward biases the LED and it lights it up. Logic 0 produces no LED current. 5 1 A 0 B 1 C 0 D g 1 LT c 1 e 0 5 V RBI Slide #3 a 1 b 0 f 1 BI Decoder a b f g e d 1 RBO d Common Cathode c
Lab 6 : LT Control Input : The decoder has 3 control inputs: LT, RBI, BI. It also has one control output: RBO. The control I/O can be used to implement various functions or they can be disabled. This section describes the Lamp Test (LT) feature. LT : is the Lamp Test input. It is active LOW. It can be connected to a switch (or control system). The user can flip the switch to test all the segments of the LED display. When the switch is in the 5 V position it disables the LT feature. DCBA (#5) controls the display. When the switch is in the 0 V position it enables the LT feature. All segments light. LT overrides the conditions at DCBA (#5). The user can now check the display for burned out segments. a a 1 0 b 1 1 0 D 5 1 C 0 B 5 v 1 A g 1 LT c 1 0 e f b f g 1 5 V RBI BI Decoder Slide #4 d RBO e 1 d Common Cathode c
Lab 6 : BI Control Input : The decoder BI input is the Blanking Input. This section describes the BI feature. BI : is the Blanking Input. It is active LOW. It can be connected to a switch (or control system). The user can flip the switch to turn off all the segments of the LED display (blank the display). When the switch is in the 5 V position it disables the BI feature. DCBA (#5) controls the display. When the switch is in the 0 V position it enables the BI feature. All segments turn off. BI overrides the conditions at DCBA (#5). 5 5 v 0 D 1 C 0 B 1 A 0 g 1 LT 0 c 1 e 0 5 V 5 RBI BI Decoder Slide #5 0 a 1 b 0 0 f 1 0 d 1 RBO a b f g e d Common Cathode c
Lab 6 : RBI and RBO Control : The RBO output is the Ripple Blanking Output. It works with RBI (Ripple Blanking Input) to blank the number 0. RBI can be connected to a switch (or control system). The user can flip the switch to turn off all the segments of the LED display (blank the display) when the number 0 is input to DCBA. All other numbers 1 … 9 are displayed normally. When the switch is in the 0 V position it enables the RBI feature. RBI blanks the display for the number “ 0”. The RBO pin (active low) outputs a logic 0 to signal that the display is blank. When the switch is in the 5 V position it disables the RBI feature. DCBA (#0) controls the display. The number “ 0” is displayed and the RBO pin outputs a logic 1. Why is this feature useful? Because it allows a user to blank leading “ 0’s” when many displays are link together to make up multiple digit numbers. This feature is described next. 0 5 v 0 D 0 C 0 B 0 A g 0 LT 1 c 0 0 e 1 5 V RBI BI Slide #6 1 a 0 1 b 0 1 f 0 Decoder 0 d 1 0 1 RBO a b f g Common Cathode c e d 01 indicates Indicates“zero” 0 is displayed is being blanked
Lab 6 : Multiple Digit Ripple Blanking Control : A multiple digit display is aesthetically more appealing to look at if leading “ 0’s” are blanked. A five digit display looks better if it shows the number 307 than it would if it showed it as 00307. The RBI and RBO control pins allow a user to blank leading “ 0’s”. The number 00307 is applied to the DCBA inputs of the display decoders. The MSD blanks the zero because RBI=0. It also outputs a zero to RBO to signal display is blank. The next MSD blanks the zero because RBI=0. It also outputs a zero to RBO. The next MSD displays the number 3 because any non-zero number is displayed. It also outputs a one to RBO to signal the display is NOT blank. The next MSD displays the number 0. It also outputs a one to RBO. The LSD always displays it’s number because RBI is always logic 1 (connected directly to 5 V). Blank Slide #7 Blank a b c d e f g RBI RBO 0 a b c d e f g RBI RBO 1 a b c d e f g RBI RBO 5 V 1 a b c d e f g RBI RBO D C B A D C B A 0000 0011 0000 0111 1
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