Fairchild MM74C911 service manual

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MM74C911
4-Digit Expandable Segment Display Controller

MM74C911 4-Digit Expandable Segment Display Controller

October 1987
Revised January 1999

General Description

The MM74C911 display controll er is an interface element
with memory that drives a 4-digit, 8- segment LED d isplay.
The MM74C911 allows individual control of any segment in
the 4-digit display. The number of segments per digit can
be expanded without any exter nal c omponent s. For exam­ple, two MM74C911’s can be cascade d to drive a 16-se g­ment alpha-numeric display.

The display controllers receive data infor mation 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, a nd WRITE ENABLE, WE, are LOW and is
latched when either CE
is not required.

A self-contained internal oscillator sequentially presents
the stored data to hi g h d r ive (100 m A typ.) 3-STATE output
drivers which directly drive the LED display. The drivers are
active when the control pin labeled SEGMENT OUTPU T
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.

or WE return HIGH. Data hold time

The digit outputs di re ctly d r ive the ba se of the d igit t ransis­tor when the control p in labeled DIGIT INPUT OUTPUT

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

DIO
inputs and the internal scanning multiplexer is disabled.

When any digit line is forced HIGH by an external device,
usually another MM74 C911, the data information for that
digit is presented to the output. In this manner, 16-segment
alpha-numeric dis plays, 24- or 32-segment d isplays, or an
array of discrete LED's can be controlled by the simple cas­cading of expandable segment display controllers. All
inputs except digit inpu ts are TTL compatible and do not
clamp input voltages above V

CC

.

Features

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

■ 4 registers addressed like RAM

■ Internal oscillator and scanning circuit

■ Direct base drive to digit transistor

■ Segment expandability without external components

■ TTL compatible inputs

■ Power saver mode—5 µW (typ.)

Ordering Code:

Order Number Package Number Package Description

MM74C991N N28B 28-Lead Plastic Dual-In-Line Package (PDIP), JEDEC MS−010, 0.600” Wide

Connection Diagram

Pin Assignments for DIP

,

Top View

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Truth Tables

MM74C911

CE

K2 K1

0 0 0 0 Write Digit 1
0 0 0 1 Latch Digit 1
0 0 1 0 Write Digit 2
0 0 1 1 Latch Digit 2
0 1 0 0 Write Digit 3
0 1 0 1 Latch Digit 3
0 1 1 0 Write Digit 4
0 1 1 1 Latch Digit 4
1 X X X Disable Writing

Input Control Output Control

Digit

Address WE Operation

Functional Description

The MM74C911 display controller is manufactured on stan­dard metal gate CMOS techno logy. A single 5V 74 series
TTL supply can be used for power and should be bypassed
at the V

The digit outputs directly drive the base of a grounded
emitter digit transistor without the need of a Darlington con­figuration. If an MM74C911 is drivi ng a digit transistor and
also supplying digit information to a cascaded MM74C911,
base resistors are nee de d i n th e dig it transistors to provide
an adequate high level to the digit inputs of the cascaded
MM74C911.

As seen in the Block Diagram, these display controllers
contain four 8-bit regi sters; any one may be random ly wr it-

pin to suppress current transients.

CC

DIO SOE Digit Lines Operation

D4 D3 D2 D1

0 0 RRRRRefresh Display
0 1 RRRRDisable Segment Outputs
1 0 0000Digits Are Now Inputs
1 0 0001Display Digit 1
1 0 0010Display Digit 2
1 0 0100Display Digit 3
1 0 1000Display Digit 4
1 1 0000Power Saver Mode

R = Refresh (digit line s se quentially pulsed)
X = Don’t Care

ten into. In normal op eratio n, the i nte rnal multiplexer scans
the registers and refr esh es th e disp lay. In cascaded opera­tion, 1 MM74C911 serves as a master refresh device and
cascaded MM74C911’s are slaved to it throu gh digit lines
operating as inputs.

The MM74C911 appea rs to a microprocessor a s memory
and to the user as a self-scan display. Since every seg­ment is under microprocessor control, great versatility is
obtained.

Low power standby operation occurs w ith both SOE

inputs HIGH. This condition forces the MM74C911 to a

DIO
quiescent state typically drawing less than 1 µA of supply
current with a standby supply voltage as low as 3V.

and

Logic Diagram

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Absolute Maximum Ratings(Note 1)

(Note 2)

Voltage at Any Pin

except Inputs −0.3V to V

Voltage at Any Input

except Digits −0.3V to +15V

Operating Temperature

Range, (T

) −40°C to +85°C

A

Storage Temperature Range −65°C to +150°C
Power Dissipation (P

) Refer to P

D

D(MAX)

+ 0.3V

CC

vs TA Graph

Operating V
Absolute Maximum V
Lead Temperature

(Soldering, 10 seconds ) 260°C

Note 1: “Absolute Maximum Rat ings” are tho se values beyond which the
safety of the device cannot be guarant eed. Exce pt for “Operating Range”,
they are not meant to imply that the device should be operated at these lim­its. The table of “Electr ical Characteristic s” provides condition s for actual
device operation.

Note 2: All voltage reference to ground.

Range 3V to 6V

CC

CC

DC Electrical Characteristics

Min/Max limits apply at −40°C ≤ TJ ≤ +85°C, unless otherwise noted

Symbol Parameter Conditions Min Typ Max Units

V

IN(1)

V

IN(0)

I

IN(1)

I

IN(0)

I

CC

I

CC

I

OUT

CMOS/LPTTL INTERFACE

V

IN(1)

V

IN(0)

OUTPUT DRIVE

I

SH

I

DH

V

OUT(1)

V

OUT(0)

θ

JA

Note 3: θJA measured in free-air with device soldered into printed circuit board.

Logical “1” Input Voltage VCC = 5V 3.0 V
Logical “0” Input Voltage 1.5 V
Logical “1” Input Current VCC = 5V, VIN = 15V 0.005 1.0 µA
Logical “0” Input Current VCC = 5V, VIN = 0V −1.0 −0.005 µA
Supply Current (Normal) VCC = 5V, Outputs Open 0.50 2.5 mA
Supply Current (Power Saver)

3-STATE Output Current VO = 5V 0.03 10 µA

Logical “1” Input Voltage VCC = 4.75V VCC − 2V
Logical “0” Input Voltage VCC = 4.75V 0.8 V

HIGH Level Segment Current VCC = 5V, VO = 3.4V

HIGH Level Digit Current VCC = 5V, VO = 3V

Logical “1” Output Voltage, VCC = 5V, IO = −360 µA4.6 V
Any Digit
Logical “0” Output Voltage, VCC = 5V, IO = 360 µA0.4V
Any Output
Thermal Resistance (Note 3) 100 °C/W

VCC = 5V, SOE, DIO = “1”,
D1, D2, D3, D4 = “0”

VO = 0V −10 −0.03

TJ = 25°C −60 −100 mA
TJ = 100°C −40 −60 mA

TJ = 25°C −10 −20 mA
TJ = 100°C −7 −10 mA
VCC = 5V, VO = 1V
TJ = 25°C −15 −40 mA
TJ = 100°C −10 −15 mA

1 600 µA

MM74C911

6.5V

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