TIL311

HEXADECIMAL DISPLAY WITH LOGIC

SODS001D – MARCH 1972 – REVISED DECEMBER 1997

2

POST OFFICE BOX 655303

POST OFFICE BOX 1443

description

This hexadecimal display contains a four-bit latch, decoder, driver, and 4

× 7 light-emitting-diode (LED)

character with two externally driven decimal points in a 14-pin package. A description of the input functions of

this device follows.

FUNCTION

PIN NO.

DESCRIPTION

LATCH STROBE INPUT

5

When low, the data in the latches follow the data on the latch data inputs. When high,

the data in the latches will not change. If the display is blanked and then restored

while the enable input is high, the previous character will again be displayed.

BLANKING INPUT

8

When high, the display is blanked regardless of the levels of the other inputs. When

low, a character is displayed as determined by the data in the latches. The blanking

input may be pulsed for intensity modulation.

LATCH DATA INPUTS (A, B, C, D)

3, 2, 13, 12

Data on these inputs are entered into the latches when the enable input is low. The

binary weights of these inputs are A = 1, B = 2, C = 4, D = 8.

DECIMAL POINT CATHODES

4, 10

These LEDs are not connected to the logic chip. If a decimal point is used, an

external resistor or other current-limiting mechanism must be connected in series

with it.

LED SUPPLY

1

This connection permits the user to save on regulated VCC current by using a

separate LED supply, or it may be externally connected to the logic supply (VCC).

LOGIC SUPPLY VOLTAGE (VCC)

14

Separate VCC connection for the logic chip

COMMON GROUND

7

This is the negative terminal for all logic and LED currents except for the decimal

points.

The LED driver outputs are designed to maintain a relatively constant on-level current of approximately 5 mA

through each LED that forms the hexadecimal character. This current is virtually independent of the LED supply

voltage within the recommended operating conditions. Drive current varies slightly with changes in logic supply

voltage resulting in a change in luminous intensity as shown in Figure 2. This change will not be noticeable to

the eye. The decimal point anodes are connected to the LED supply; the cathodes are connected to external

pins. Since there is no current limiting built into the decimal point circuits, limiting must be provided externally

if the decimal points are used.

The resultant displays for the values of the binary data in the latches are as shown below.

0

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15