lab 6 :digital display decoder: 7 segment led display slide #2 slide #3 slide #4 slide #5 slide #6...
TRANSCRIPT
Lab 6 :Digital Display Decoder:
7 Segment LED displaySlide #2
Slide #3
Slide #4
Slide #5
Slide #6
Slide #7
Display Decoder Fundamentals
LT Control Input
BI Control Input
Ripple Blanking:
RBI and RBO
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…
a
b
c
d
e
f
g
Common Catthode
1
1
1
0
0
0
0
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
b
c
d
e
f
g
Common Anode
0
0
0
1
1
1
1
5V
Slide #2
a
b
c
d
e
f
g
Common Cathode
a
b
c
f
g
e
d
A
B
C
D
LT
RBIBI
Decoder
Lab 6 : 7 Segment DecoderThe 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.
5V
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.
1
0
1
0
1
0
1
1
10
1
The number 5 is applied to the input. D is MSB and A is LSB.
5
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.
Slide #3 RBO
a
b
c
d
e
f
g
Common Cathode
a
b
c
f
g
e
d
D
C
B
A
LT
RBIBI
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.
5V
0
1
0
1
1
0
1
1
10
1
55v
5V
0
1
0
1
1
1
1
1
11
1
55v
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.
Slide #4
RBO
a
b
c
d
e
f
g
Common Cathode
a
b
c
f
g
e
d
D
C
B
A
LT
RBIBI
Decoder
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).
5V
0
1
0
1
0
0
0
0
00
0
5
5v
5
0
1
0
1
1
0
1
1
10
1
5
5v
5V
Slide #5
RBO
a
b
c
d
e
f
g
Common Cathode
a
b
c
f
g
e
d
D
C
B
A
LT
RBIBI
Decoder
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 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.
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.
0
0
0
0
1
1
1
0
11
1
0
5v 5V
1 Indicates 0 is displayed
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.
Slide #6
RBO
0
0
0
0
0
0
0
0
00
0
0
5v 5V
0 indicates “zero” is being blanked
01
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.
a b c d e f g
D C B A
RBI RBO
a b c d e f g
D C B A
RBI RBO
a b c d e f g
D C B A
RBI RBO
a b c d e f g
D C B A
RBI RBO
a b c d e f g
D C B A
RBI RBO
5V
0 0 0 0 0 0 0 0
0 0 1 1
0 0 0 0
0 1 1 1
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.
10
Blank
0
Blank
The next MSD displays the number 0. It also outputs a one to RBO.
1
The LSD always displays it’s number because RBI is always logic 1 (connected directly to 5V).
1
Slide #7