October 1987

Revised January 1999

© 1999 Fairchild Semiconductor Corporation

DS005915.prf

www.fairchildsemi.com

MM74C911

4-Digit Expandable Segment Display Controller

General Description

The MM74C911 display controller is an interface element

with memory that drives a 4-digit, 8-segment LED display.

The MM74C911 allows individual control of any segment in

the 4-digit display. The number of segments per digit can

be expanded without any external components. For exam-

ple, two MM74C911’s can be cascaded to drive a 16-seg-

ment alpha-numeric display.

The display controllers receive data information through 8

data lines a, b…DP, and digit information through 2

address inputs K1 and K2. The input data is written into the

register selected by the address information when CHIP

ENABLE, CE, and WRITE ENABLE, WE, are LOW and is

latched when either CE or WE return HIGH. Data hold time

is not required.

A self-contained internal oscillator sequentially presents

the stored data to high drive (100 mA typ.) 3-STATE output

drivers which directly drive the LED display. The drivers are

active when the control pin labeled SEGMENT OUTPUT

ENABLE, SOE, is LOW and go into 3-STATE when SOE is

HIGH. This feature allows for duty cycle brightness control,

or for disabling the output drive for power conservation.

The digit outputs directly drive the base of the digit transis-

tor when the control pin labeled DIGIT INPUT OUTPUT,

DIO, is LOW. When DIO is HIGH, the digit lines turn into

inputs and the internal scanning multiplexer is disabled.

When any digit line is forced HIGH by an external device,

usually another MM74C911, the data information for that

digit is presented to the output. In this manner, 16-segment

alpha-numeric displays, 24- or 32-segment displays, or an

array of discrete LED's can be controlled by the simple cas-

cading of expandable segment display controllers. All

inputs except digit inputs are TTL compatible and do not

Features

s Direct segment drive (100 mA typ.) 3-STATE

s 4 registers addressed like RAM

s Internal oscillator and scanning circuit

s Direct base drive to digit transistor

s Segment expandability without external components

s TTL compatible inputs

s Power saver mode—5

µW (typ.)

Ordering Code:

Connection Diagram

Pin Assignments for DIP

Top View

Order Number

Package Number

Package Description

MM74C991N

N28B

28-Lead Plastic Dual-In-Line Package (PDIP), JEDEC MS

−010, 0.600” Wide