SCE5780

2006-01-23

10

Row Strobing

The SCE578X allows a high frequency external oscillator source

to drive the display. Data bit, D4, in the control word format con-

trols the prescaler function. The prescaler allows the oscillator

source to be divided by 16 by setting D4=1. However, the pres-

caler should not be used, i.e., when using the internal oscillator

source.

The Software Clear (C0

clears the Address Register and the RAM. The display is blanked

and the Character Address Register will be set to Character 0. The

internal counter and the Control Word Register are unaffected.

The Software Clear will remain active until the next data input cycle

is initiated.

Multiplexer and Display Driver

The eight characters are row multiplexed with RAM resident col-

umn data. The strobe rate is established by the internal or external

MUX Clock rate. The MUX Clock frequency is divided by a 320

counter chain. This results in a typical strobe rate of 768 Hz. By

pulling the Clock SEL line low, the display can be operated from an

external MUX Clock. The external clock is attached to the CLK I/O

connection.

An asynchronous hardware Reset (pin 24) is also provided. Bring-

ing this pin low will clear the Character Address Register, Control

Word Register, RAM, and blanks the display. This action leaves the

display set at Character Address 0, and the Brightness Level set at

100%, prescaler ÷1.

Electrical and Mechanical Considerations

Thermal Considerations

The display’s power usage may need to be reduced to operate at

high ambient temperatures. The power may be reduced by lower-

ing the brightness level, reducing the total number of LEDs illumi-

nated, or lowering V

supply, has little effect on the power dissipation of the display and

is not considered when determining the power dissipation.

To determine the power deration with a given ambient tempera-

ture, use the following formula:

where:

T

P

θ

To determine the power dissipation of the display, use the following

formula:

where:

N=number of LEDs on

I

RB=relative brightness level

A typical thermal resistance value (

θ

when mounted in a socket soldered on a 1.57 mm (0.062") thick

PCB with 0.5 mm (0.020"), 1 ounce copper traces and the display

covered by a plastic filter. The display’s maximum IC junction tem-

perature is 125°C. Power Deration Curve is based on these typical

values.

Power Deration Curve (

θ

V

ground. V

the power for the LEDs. By separating the two supplies, V

V

0

4

5

6

Columns

12 3 4

Load

Row

Load Row 0

1

2

3

0

Columns

01 23 4

Columns

01 2 34

Load Row 1

Load Row 2

Load Row 5

Columns

Columns

01 2 3 40

Columns

12 3 4

01

Load Row 4

Load Row 3

Columns

IDXX5192

23 4

01 2 34

Load Row 6

6

5

3

4

2

0

1

6

5

3

4

2

0

1

6

5

3

4

2

0

1

6

5

3

4

2

0

1

6

5

3

4

2

0

1

6

5

3

4

2

0

1

Software Clear

Op code

D7 D6

Control Word

D5 D4

D3

D2

D1

D0

Hex

Operation

11

0

0

00

00

C0

CLEAR

T

jmax

T

A

P

D

θ

ja

⋅

+

=

PD

N I

RB

⋅

⁄

⋅

=

IDDG5333

-40

0

P

W

-20

0

20

40

60

˚C 100

0.5

1.0

1.5

2.0

2.5

T