HT16562

Rev. 1.20

5

December 17, 2010

Functional Description

VFD Display Driving

The display can directly drive VFD signals dynamically

and does so at a 1/2 duty cycle rate. The clock will be

displayed in a 12-hour format with the hours ranging

from 1 to 12 and minutes from 00 to 59. If the most sig-

nificant numeral is zero then the display will be extin-

guished.

A single 7-segment display is shown below showing

the illumination 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 grids and seg-

ments are shown below, however it should be noted

that the fourth segment only requires two of its seg-

ments to be driven. Additionally it should be noted that

the colon can also be illuminated.

Other Pin Functions

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

circuits 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

²1:00² output.

The BLANK pin, if pulled low will extinguish the display.

Note that during the time when the BLANK pin is low, the

HS,MS and ZA pins will be automatically disabled by

the device and have no function.

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.

The TEST pin is used during manufacturing for device

testing purposes and should not be connected to any

external circuitry.

Two illumination level set pins, DIM1 and DIM2, are pro-

vided to give control over the display brightness level, as

shown in the following table.

Switch Pin

Name

Operating mode

Dim1

Dim2

L

L

f=256Hz, 1/2 duty (50% display)

H

L

f=256Hz, 1/4 duty (25% display)

L

H

f=256Hz, 1/8 duty (12.5% display)

H

H

f=256Hz, 1/16 duty (6.25% display)

Device Functions

Although the device is provided with an external reset

pin A/C, the device will in fact reset itself when power

is applied, eliminating the need for external reset com-

ponents. The usual provision of an external capacitor

is not required as an internal reset capacitor is inte-

grated within the device.

An internal regulator function is also integrated within

the device providing a stable voltage power supply

source for the internal circuits. This allows the device

to operate with a wide external power supply ranging

from 4V to 18V.

The device contains circuits which are connected to

input pins HS,MS and ZA to remove chatter of less

than 31.25ms.

The basic time base frequency for this device is deter-

mined by an external 4.194304MHz crystal. When an

external crystal along with two small external capaci-

tors are connected to the two oscillator XT pins, the in-

ternal oscillator circuit will ensure generation of the

correct time base signals. The oscillation frequency,

although determined by the external crystal fre-

quency, will also be influenced by the external capaci-

tors, the crystal inherent capacitance and the residual

capacitance of the external PCB tracks. To ensure ac-

curate frequency generation, the crystal specification

should be carefully consulted and the external capaci-

tors and crystal should be placed as close to the de-

vice as possible.



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

c o l

c o l

c o l o n

G R 1

G R 2

2 a

2 b

2 c

2 d

2 e

2 f

2 g

1 a

1 b

1 c

1 d

1 e

1 f

1 g

3 a

3 b

3 c

3 d

3 e

3 f

3 g

4 b

4 c