Real-Time Clock plus RAM with Serial Interface CMOS

TheMC68HC68T1 HCMOS Clock/RAM peripheral contains a real–time clock/calendar,a 32x 8 static RAM, and a synchronous, serial, three–wire interface for communication with a microcontroller or processor. Operating in a

burstmode, successive Clock/RAM locations can be read or written using only asingle starting address. An on–chiposcillator allows acceptance of a selectable crystal frequency or the device can be programmed to accept a

50/60 Hz line input frequency.

• Full Clock Features — Seconds, Minutes, Hours (AM/PM), Day–of–Week, Date, Month, Year (0 – 99), Auto Leap Year

• 32–Byte General Purpose RAM

• Direct Interface to Motorola SPI and National MICROWIRE
Serial Data Ports

• Minimum Timekeeping Voltage: 2.2 V

• Burst Mode for Reading/Writing Successive Addresses in Clock/RAM

• Selectable Crystal or 50/60 Hz Line Input Frequency

• Clock Registers Utilize BCD Data

• Buffered Clock Output for Driving CPU Clock, Timer, Colon, or LCD Backplane

• Power–On Reset with First Time–Up Bit

• Freeze Circuit Eliminates Software Overhead During a Clock Read

• Three Independent Interrupt Modes — Alarm, Periodic, or Power–Down

• CPU Reset Output — Provides Orderly Power–Up/Power–Down

• Watchdog Circuit

• Pin–for–Pin Replacement for CDP68HC68T1

• Chip Complexity: 8500 FETs or 2125 Equivalent Gates

• Also See Application Notes ANE425 “Use of the MC68HC68T1 RTC with M6805 Microprocessor”, AN457 “Providing a Real–Time Clock for the MC68302”, and AN1065 “Use of the MC68HC68T1 Real–Time Clock with

Multiple Time Bases”