CD4511 seven-segment driver
Four wires in, one lit digit out: a BCD to seven-segment decoder for a common-cathode display.
The 4511 takes a number from 0 to 9 in binary on A to D and lights the segments
of a common-cathode seven-segment display to show it, with no clock and no code. It
also holds a digit (a latch), blanks the display on command and has a lamp test.
Aliases: 4511, CD4511BE, MC14511, HEF4511, BCD to 7-segment decoder, display driver.
Pins
| Pin | Name | What it does |
|---|---|---|
| 7, 1, 2, 6 | A, B, C, D |
The BCD input. A is the 1s bit, D the 8s. |
| 13, 12, 11, 10, 9, 15, 14 | a to g |
Segment outputs, high to light a segment. |
| 3 | LT |
Lamp test, active low. Low lights every segment. |
| 4 | BI |
Blanking, active low. Low turns every segment off. |
| 5 | LE |
Latch enable. Low: the display follows the inputs. High: it holds the last code. |
| 8 | VSS |
Ground. |
| 16 | VDD |
Supply, 3 V to 18 V. |
Truth table
LE |
BI |
LT |
D C B A |
Display |
|---|---|---|---|---|
| x | x | 0 | x | 8 (every segment on) |
| x | 0 | 1 | x | Blank |
| 0 | 1 | 1 | 0000 to 1001 | The digit 0 to 9 |
| 0 | 1 | 1 | 1010 to 1111 | Blank |
| 1 | 1 | 1 | x | The code that was there when LE went high |
| Digit | Segments lit |
|---|---|
| 0 | a b c d e f |
| 1 | b c |
| 2 | a b d e g |
| 3 | a b c d g |
| 4 | b c f g |
| 5 | a c d f g |
| 6 | c d e f g |
| 7 | a b c |
| 8 | a b c d e f g |
| 9 | a b c f g |
The 4511's 6 and 9 have no tails: 6 is missing segment a and 9 is missing segment
d. That is how you tell a 4511 display from one driven by a microcontroller.
Properties
None.
What the model gets right
The outputs source current. Each segment output is an NPN emitter follower that
can source up to 25 mA, so a high output sits about 0.6 V under VDD and sags a
little more under load: the model is VDD minus 0.6 V behind 35 ohms, a straight
line through the MC14511B data sheet's typical output voltages from 5 to 25 mA. A
low output is only the weak CMOS pull-down, as on the 4017. A segment still needs a
series resistor, typically 330 ohms to 1 k at 5 V.
Delays come from the data sheet, per path and direction. At 5 V: 640 ns for a segment to light and 720 ns to go out after a data change; 600 and 485 ns after blanking changes; about 310 ns after lamp test changes. They shorten with the supply (250 and 290 ns for data at 10 V) and are interpolated in between.
An unknown input only clouds the segments it could change. With A, B and C
low and D floating, the code is 0 or 8, which differ only in segment g: every
other segment is known and lit, and only g shows as unknown.
What it does not model
No setup or hold time on the latch. No current limit on the outputs and no damage from running a segment without a resistor; the only thing limiting the current then is the 35 ohms of the model. Below 5 V the delays are held at the 5 V figures. Common-anode displays need a different chip (the 4543 or a 74HC247) and will not light from this one, as on the bench.
Common mistakes
Leaving LT or BI floating (tie both to VDD), or LE floating (tie it to VSS),
and using a common-anode display.
See it in action
BCD display sets a digit with a 4-way DIP switch and shows it on a seven-segment display through a 4511. Open it at /templates.