From the Ricoh datasheet...
FEATURES
• Connected directly to CPU • 4bit bidirectional data bus : D0 - D3 • 4bit address input : A0 - A3
• Built-in clock counter (hour, minute, second) and calendar counter (leap year, year, month, day, day-of-the-week)
• Supports both 12-hour AM/PM clock and 24-hour clock
• All clock data expressed in BCD codes • ±30 second adjustment function
• Backed up by batteries (minimum:2.2V) etc.
