TIL311

HEXADECIMAL DISPLAY WITH LOGIC

TAOS058 − JANUARY 2004

5

The

LUMENOLOGY

r Company

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Copyright

E 2006, TAOS Inc.

www.taosinc.com

PRINCIPLES OF OPERATION

TTL-level four-bit binary data is applied to Latch Data Inputs A through D. As long as the Latch Strobe Input is

low, latch output follows the input data. Latch output data is decoded and sent to the display LEDs to form the

corresponding characters. When the Latch Strobe Input goes high, input data is stored in the latch and the

display does not change.

The resulting character displays for the values of the binary data in the latch are shown in Figure 4.

0

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

Figure 4. Display Character Configurations

While the Blanking Input is held low, the display shows the character corresponding to the data at the latch

output. When the Blanking Input goes high, drive to the character display LEDs is removed and the display is

blanked (except for the decimal points, which are independent and externally driven). Data in the latch and

operation of the device logic elements are not affected by blanking the display. A repetitive variable-width pulse

can be applied to the Blanking Input to adjust the apparent brightness of the display.

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 the logic

supply voltage, resulting in a change in luminous intensity as shown in Figure 2. This change is not 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, current limiting must be provided externally if the

decimal points are used.