HT16565

Rev. 1.00

6

February 7, 2007

Three illumination level set pins, DIM, CONT1 and CONT2 are provided to give control over the display brightness

level, as shown in the following table.

Switch Pin Name

Operating mode

DIM

CONT1

CONT2

0

(or Open)

*

*

100% duty display

1

0

(or Open)

1

(or Open)

25% (1/4) duty display at 4096Hz

1

0

(or Open)

0

12.5% (1/8) duty display at 4096Hz

11

1

(or Open)

6.25% (1/16) duty display at 4096Hz

Note:

²1² high level, ²0² low level, ²*² don¢t care

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.

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 pins, the inter-

nal 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 taken into account and care taken to place

the external capacitors and crystal as close to the de-

vice as possible.

Time Adjustment Operation

Both the minutes and hour displays can be adjusted

separately or both together in a fast forward format.

The hour set pin, HS, and the minutes set pin, MS, are

used to make these adjustments. Both of these pins

are connected to internal pull-low resistors. Each time

one of these lines is pulled high, the respective hour or

minute value will increment by one, also if the line is

continuously held high then the respective value will

increment automatically at a rate of 2Hz. Both values

will increment together if both lines are pulled high si-

multaneously. Note that no carry functions will be im-

plemented when either the hour or minute value

overflows.

A zero adjust function is also included within the de-

vice and is controlled by the ZA pin. This pin is con-

nected to an internal pull low resistor. Pulling this line

high will reset both the internal minutes and seconds

value, however the way in which the display is reset

depends upon the present value of display. If the min-

ute value is presently less than 30 the only the second

and minute values will be reset to zero and the hour

value remain unchanged. However if the minute value

is presently at a value of 30 or higher then when the

zero adjustment function is executed, a carry will be

implemented and the hour value will be increment by

one. The following table illustrates a few examples of

this operation.

Zero Adjust Examples

Present Time

After Zero Adjust

Hr.

Min.

Sec.

Hr.

Min.

Sec.

1

30

00

2

00

00

2

00

00

2

00

00

2

29

59

2

00

00

2

30

00

3

00

00

2

59

59

3

00

00

3

29

59

3

00

00