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.

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 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. 2. Forward voltage: HTC2500 can drive LED displays with forward voltage rating from 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 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 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 to 720K.

Notes Says Hi for one second. We are still investigating if it means High Tech Chips or just Hi. Lading zero HH is not displayed. - characters indicates that clock is in one of setting modes. Same As Above. Same As Above. Requires backup battery.

Set: Ignored. Mode: Go to Set Hour mode. Set: increment HH. Mode: Go to Set Minute mode Set: increment MM. Mode: Go to Set Second mode Set: zero SS. Mode: Go to Normal mode 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. SS 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.