HT16565

Rev. 1.00

5

February 7, 2007

Functional Description

VFD Display Driving

The device can directly drive VFD clock panels dynami-

cally. The clock will be displayed in a 24-hour format with

the hours ranging from 0 to 23 and and minutes from 00

to 59. If the most significant numeral is zero then the dis-

play will be extinguished.

A 7-segment display is shown below showing the illu-

mination pattern for each numeral.

As the device is designed for clock applications, four

7-segment displays are required to display the correct

time output. The connections for the segments are

shown below, however it should be noted that the

fourth segment only requires two of its segments to be

driven.

Other Pin Functions

The external reset pin A/C is used to reset the internal

circuit of the device. When this pin is pulled low the de-

vice will be reset, when the pin is allowed to go high, via

its internal pull-high resistor, then the display will indi-

cate a

²0:00² output.

In the open status, the SE pin is held to

²high² level by a

pull-high resistor, enabling the inputs from MS, HS and

ZA pins. These inputs become invalid by setting this pin

to a

²low² level externally.

The 64Hz pin allows monitoring of the system frequency

to allow frequency adjustments to be executed. As the

name suggests, this output pin will continuously output

a frequency of 64Hz.

In the open status, the TEST1 and TEST2 pins are kept

at a

²0² level by pull-down resistors.

In the open status, the TEST3 and TEST4 pins are kept

at a

²1² level by pull-up resistors.

The Test pin function is as shown in the following table.



7 - S e g m e n t s

A

B

C

D

E

F

G

d i g i t 4

d i g i t 3

d i g i t 2

d i g i t 1

1 H z

1 H z

a 2

b 2

c 2

d 2

e 2

f 2

g 2

a 1

b 1

c 1

d 1

e 1

f 1

g 1

a 3

b 3

c 3

d 3

e 3

f 3

g 3

b 4

c 4

a 4

d 4

e 4

g 4

TEST select function 1

Switch Pin Name

Operating mode

TEST1

TEST2

TEST3

0

(or Open)

0

(or Open)

1

(or Open)

Normal function.

F(Pulse)

1

1

(or Open)

Input pulses to the 16.384kHz system of the circuit.

1

F(Pulse)

1

(or Open)

Input pulses to the 16.384kHz system of the circuit.

1

F(Pulse)

0

Input pulses to the 64Hz system of the circuit.

F(Pulse)

1

0

Input pulses to the 64Hz system of the circuit.

F(Pulse)

0

(or Open)

0

Input pulses for the minute and hour counters, which advances 1 count

with 1 pulse. No carry functions for hour and minute counters.

TEST select function 2

Switch Pin Name

Operating mode

TEST3

DIM

CONT1

CONT2

0

F(Pulse)

**

The pulse widths of the all segment outputs are controlled

by the pulse width of the DIM signal

0

0

*

*

Sets all segment outputs to high impedance

Note:

²*² Indicates that the input level can be ²0² and ²1²