CD4511: the BCD to 7-segment latch decoder driver, live

The CD4511 turns a BCD digit on D C B A into the seven segment signals a to g for a common-cathode display, with active-high outputs (1 lights a segment). It adds an input latch (LE), a lamp test (LT) and blanking (BL), and it blanks the display for codes above 9. This live circuit follows its truth table and drives a 7-segment display.

TI's datasheet (from Harris Semiconductor) describes BCD-to-7-segment latch decoder drivers with outputs that can source up to 25 mA, enough to drive LEDs directly. The latch is the feature the 74LS47 lacks: while LE is low the four latches are transparent and the display follows D C B A; when LE goes high they hold the last code, so the inputs can change, or be shared between several digits, without the display flickering. LT low lights all seven segments, whatever the other inputs, to test the display; BL low (with LT high) turns them all off, which also lets you dim the display by pulsing it. Like the 74LS47, it draws 6 without its top segment and 9 without its bottom one, and unlike the 74LS47 it shows nothing at all for codes 10 to 15. Each segment here is decoded from the latched bits as a minimal sum of products, gated by BL and overridden by LT. The live circuit opens showing 0 with LE low. Before the page is built, all 64 combinations of BL, LT and D C B A are checked with the latch open, and then the latch: LE high holds a 3 while the inputs change to 8, and LE low shows the 8.

Big circuit: pinch, scroll or tap + to zoom in, then drag to move around.

Live circuit: click the inputs to toggle them and watch the outputs update. It runs the real simulator, right here on the page.

Open this circuit in the lab →

What you need

4× D latch: the input latches, transparent while LE is low (enable = NOT LE)
4× NOT: the latched bits inverted, for the decode
7× sum of products: one minimal SOP per segment over the latched D C B A (ANDs and ORs)
7× AND + 7 OR: each segment: (BL AND decode) OR NOT LT
2× NOT: NOT LE and NOT LT

Step by step

Place inputs LE, BL, LT, D, C, B, A, probes a to g, and a 7-segment display.
Latch each BCD input in a D latch enabled by NOT LE.
Decode each segment from the latched bits as a minimal sum of products, lit for 0 to 9 only (6 and 9 without tails).
Gate each segment: seg = (BL AND decode) OR NOT LT, and wire a to g to the display.
Count D C B A from 0000 to 1001, then set LE high and change the inputs: the digit stays. Try LT = 0 (an 8) and BL = 0 (blank).

CD4511 truth table

LE	BL	LT	D C B A	a b c d e f g	Display
X	X	0	X X X X	1 1 1 1 1 1 1	8 (lamp test)
X	0	1	X X X X	0 0 0 0 0 0 0	blank
0	1	1	0 0 0 0	1 1 1 1 1 1 0	0
0	1	1	0 0 0 1	0 1 1 0 0 0 0	1
0	1	1	0 0 1 0	1 1 0 1 1 0 1	2
0	1	1	0 0 1 1	1 1 1 1 0 0 1	3
0	1	1	0 1 0 0	0 1 1 0 0 1 1	4
0	1	1	0 1 0 1	1 0 1 1 0 1 1	5
0	1	1	0 1 1 0	0 0 1 1 1 1 1	6
0	1	1	0 1 1 1	1 1 1 0 0 0 0	7
0	1	1	1 0 0 0	1 1 1 1 1 1 1	8
0	1	1	1 0 0 1	1 1 1 0 0 1 1	9
0	1	1	1010 to 1111	0 0 0 0 0 0 0	blank
1	1	1	X X X X	held	the code latched while LE was 0

CD4511 pinout

Pin	Name	Pin	Name
1	B	16	VDD
2	C	15	f
3	LT (active low)	14	g
4	BL (active low)	13	a
5	LE / STROBE	12	b
6	D	11	c
7	A	10	d
8	VSS	9	e

X means the input does not matter. The truth table, features and 16-pin pinout are from TI's CD4511B datasheet (SCHS072B), checked 2026-10-25; it runs from 3 V to 18 V and is, in the datasheet's words, similar to the MC14511. For common-anode displays the usual choice is an active-low driver such as the 74LS47.

You can also read the full theory in the lesson on binary-coded decimal. Prefer to build it yourself from scratch? Open the digiwleea lab and place the gates on the canvas, or start from the logic gate simulator.

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Each of these is one step from a transistor to a working CPU. Build every gate from CMOS transistors and work all the way up in the free digiwleea lab, with the free theory reference alongside.

Open the CD4511 BCD to 7-segment decoder in the lab →

Frequently asked

What does the CD4511 do?

It decodes a 4-bit BCD digit into the seven segment signals for a common-cathode 7-segment display, with active-high outputs that can source enough current to drive LEDs. It also has an input latch, a lamp test and a blanking input.

Is the CD4511 for common anode or common cathode displays?

Common cathode: its outputs go high to light a segment, sourcing current into the segment, whose cathode goes to ground. For common-anode displays use an active-low decoder like the 74LS47.

What does the LE pin on the CD4511 do?

LE (latch enable, or strobe) controls the input latches. While LE is low the display follows the BCD inputs; when LE goes high the current code is held, so the inputs can change without changing the display.

What does the CD4511 show for inputs above 9?

Nothing: the datasheet's truth table blanks all seven segments for the illegal codes 1010 to 1111.

What is the difference between the CD4511 and the 74LS47?

The CD4511 is CMOS with active-high outputs for common-cathode displays, an input latch, and blank outputs above 9. The 74LS47 is TTL with active-low open-collector outputs for common-anode displays, ripple blanking for leading zeros, and odd symbols for 10 to 14.