Transcript Document
Lab 6 :Digital Display Decoder:
7 Segment LED display Display Decoder Fundamentals LT Control Input BI Control Input RBI and RBO 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 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…
Common Cathode
. It lights 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 a
1 1 0
f
0 1 0
e
0
g b c
Common Catthode 0 0 1
f
1 0 1
e
1
g b c 5V
Common Anode
d d
Slide #2
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 explained later.
Active Low
control inputs LT, RBI, BI. They will be disabled for now and 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.
a 5 1 0 1 0 5V
A B C D LT RBI a f b
1 0 1
g
1
c e
1 0
d
1 f e g b c
Common Cathode
d
Slide #3 Decoder
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
B A D C f a b g
0 1
LT RBI BI Decoder c e d RBO
1 0 f e g d b c
Common Cathode Slide #4
Lab 6 : BI Control Input :
The decoder feature.
BI
input is the Blanking Input. This section describes the BI 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).
a 5
B A D C f a b g
0 0
LT RBI BI Decoder c e d RBO
0 0 f e g d b c
Common Cathode Slide #5
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.
a
D a C B f b
f b
A LT g c e
1 1 e g c
Common Cathode RBI BI d RBO
d
Slide #6 Decoder
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 5V).
Blank Blank
Slide #7 a b c d e f g RBI RBO D C B A 0 0 0 0 0 a b c d e f g RBI RBO D C B A 0 0 0 0 0 a b c d e f g RBI RBO D C B A 1 0 0 1 1 a b c d e f g RBI RBO D C B A 1 5V a b c d e f g RBI RBO D C B A 1 0 0 0 0 0 1 1 1