This clock is made of two line slices, each slice is microprocessor controlled with I2C segment drivers, using an 8MHz quartz crystal oscillator. The RS-232 serial (5 volt level) is used to comunicate between boards. A 1 Farad capacitor provides short term (15 minutes) hold up to retain time through short power outages.
There is a large list of world and US cities with daylight savings times that can be loaded into the display locations. The menu systems allows any text to be entered as a city name, and the daylight savings dates can be set.
The locations and settings are stored in EEROM so they are kept through any power outage.