HIGH TECH

CHIPS, INC.

12/26/99

General Description

HTC2500 is simple clock IC built by using
our micro RTOS.
Features:

Operation from low cost low power

32768Hz crystal.

Supports backup power supply in case of

main power failure.

Simple intuitive interface for adjusting clock.

Minimum external components.

Schematics below show typical connection
diagram. HTC2500 uses four digits common
cathode seven segment display.

PDIP, SOIC

HTC2500

CAT_2

CAT_1

CAT_3

CAT_0

XIN

RESET

XOUT

GND

VDD

SEG_A COLON

SEG_B

SEG_G

SEG_C

SEG_F

SEG_D

SEG_E

620R

R10

620R

R11

620R

R12

620R

R13

620R

R14

620R

R16

R1
10K

10K

100n

10K

BAV20DICT-ND

32768Hz

R15

47K

12.5pF

100n

10K

DP1

DP2

AL2

AL1

LN543RKN8

CAT_1

DP1+

CAT_2

CAT_3

DP2+

CAT_4

AL2

A1A2

AL1

DP2

DP1

AMPM

SW2

MODE

SW1

SET

10uF

MAIN PWR 5V

PWR

GND

BACKUP 9V

PWR

GND

HTC2500

SEG_A

SEG_B

SEG_C

SEG_D

SEG_E

SEG_F

SEG_G

CAT_0

CAT_1

CAT_2

CAT_3

VDD

RESET

COLON

GND

XIN

XOUT

100K

5.6V

BAV20DICT-ND

HIGH TECH

CHIPS, INC.

12/26/99

Crystal Selection
Please note that R15, C4 and C5 values shown in schematics above are for reference only.
Consult manufacturer of Y1 crystal used for recommended values. Precision of clock depends
on crystal used and values selected for above components. When choosing crystal make sure
that it has +-20PPM tolerance in temperature range used. For example crystal rated +-20 PPM
in temperature range of 10 to +60 degrees Celsius is a good choice.

Switch Selection
Set and Mode switch inputs are internally de-bounced. This eases switch selection. You can
even use two wires laid out in parallel and conductivity of your skin would be enough to make
it work as a switch. Also conductive rubber could be used to design your own decorative
switch.

Display Selection
Several factors should be considered in seven-segment LED display selection.
1.

Average Luminous Intensity (in uCd) at 3.5ma. This parameter determines brightness of
display and varies widely even in one device family.

Forward voltage: HTC2500 can drive LED displays with forward voltage rating from 1.6 to
4.2V(this range covers most of LED's and seven segment displays). This rating corresponds
to number of LED's used in each segment and color of LED. For example red LED has
typical 2.0V forward voltage. This means we can use two red LED's in series for each
segment if we are building our own custom display.

Main and Backup Power Selection
Voltage on VDD pin should be in range from +3.0 to +6.2V. Example of good Backup power
might be Lithium battery (3V). In case of using 9V battery for backup we should replace D1 in
schematics above with Zener connected backwards. We use Zener for voltage drop. Voltage
rating for Zener in this case should be 9V-MPV-0.5V volts minimum (MPV stands for main
power voltage and 0.5 is D1 diode forward drop voltage). HTC2500 is using about 0.12mA
current from 5V(depends on crystal selection) in power down mode. If we are using 9V alkaline
battery with 500mA/H capacity for backup power it will keep HTC2500 alive for about 138
days. Please note that we don't guaranty this value because it depends on clock design
specifications and component selection that are out of our control.

R5 and C3 value selection
Values of R5 and C3 are for reference only. It might need adjustment and depends on Crystal
selection. Basic rule of thumb is that Reset line should be held below 0.85*VDD until clock
generator is started (depends on crystal used). R5 value could be in the range of 0 to 720K.

HIGH TECH

CHIPS, INC.

12/26/99

Modes of operation

Mode

Display
characters

Notes

Key Behavior

Start up

Says Hi for one
second. We are still
investigating if it
means High Tech
Chips or just Hi.

Ignored

Normal

HH : MM

Lading zero in HH is
not displayed.

Set: Ignored.
Mode: Go to Set Hour mode.

Set Hour

HH : - -

- - characters
indicates that clock
is in one of setting
modes.

Set: increment HH.
Mode: Go to Set Minute mode

Set Minute

- - : MM

Same As Above.

Set: increment MM.
Mode: Go to Set Second mode

Set Second

- - : SS

Same As Above.

Set: zero SS.
Mode: Go to Normal mode

Power
Saving

None!

Requires backup
battery.

None! Wakes up in Normal
mode once main power is
restored.

Abbreviations used
HI

Still under investigation. We would like to hear from you on this subject. Please use
Feedback form from our web site (

www.hightechips.com

) for replay.

MM Minutes.
HH

Hours. Please note that we are using 12-hour format in our clock. Leading zeroes are not
displayed in HH.

Seconds.

G elements of seven segment display.

Set and Mode key behavior
In all modes of operation display is changed when key is released. This is true for both keys. If
you hold any key for more then 2 seconds display will change much faster. This functionality is
useful when setting minutes and hours.

HIGH TECH

CHIPS, INC.

12/26/99

Signal description:

Abbreviations used: O - output, I - input, P - power.

Name

Pin I / O Description

Name

Pin I / O Description

CAT_ 2

Cathode 2

NOTE 1

SEG_E

Display Segment E

NOTE 2

CAT_3

Cathode 3

NOTE 1

SEG_F

Display Segment F

NOTE 2

Not used. Connect to
VCC.

SEG_G

Display Segment G

NOTE 2

#RESET

Reset

NOTE 4

COLON

Colon output

NOTE 2

GND

Power ground

VDD

Power

NOTE 5

SEG_A/
SET

I/O

Display Segment A

NOTE 2

XOUT

Clock generator output.

SEG_B/
MODE

I/O

Display Segment B

NOTE 2

XIN

Clock generator input.

SEG_C/

PWR_OK

I/O

Display Segment C

NOTE 3

CAT_ 1

Cathode 1

NOTE 1

SEG_D

Display Segment D

NOTE 2

CAT_0

Cathode 0

NOTE 1

Note 1:
This outputs can sink up to 25mA current. Voltage on this pin at 25mA is 1V.
Note 2:
This output can source up to 20mA. Limiting resistors should be used with these outputs. When
number eight is displayed we consume maximum power and CAT_N sink current should be
limited to maximum 25mA. So each output should source no more then 25mA/7=3.6mA. In
order to find appropriate values for those resistors
We subtract Forward Voltage rating

value of our display from VCC and divide that by 3.6mA.

Forward Voltage value

is depending on display used. Please consult manufacturers data sheet

for chosen display.
Note 3:
This output can source up to 20mA. Limiting resistor should be used with this output. This
output should not source more then 5mA. PWR_OK (Power OK) pin should be connected to
Main power via resistor. Value of resistor should be from 1K to 100K. If this pin connected to
VCC without power limiting resistor excessive damage to the part will result.
Note 4:
Values of R5 and C3 are for reference only. It might need adjustment and depends on Crystal
selection. Basic rule of thumb is that Reset line should be held below 0.85*VDD until clock
generator is started (depends on crystal used). R5 value could be in the range of 0 to 720K.

Ð­Ð»ÐµÐºÑ‚Ñ€Ð¾Ð½Ð½Ñ‹Ð¹ ÐºÐ¾Ð¼Ð¿Ð¾Ð½ÐµÐ½Ñ‚: HTC2500SC

ÐÐ»ÐµÐºÑ‚Ñ€Ð¾Ð½Ð½Ñ‹Ð¹ ÐºÐ¾Ð¼Ð¿Ð¾Ð½ÐµÐ½Ñ‚: HTC2500SC