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motorola-mc68hc68t1p-rtc

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Important Note

This entire repo was AI created - including all of the data within. The intent was to A) help me with my personal electronics inventory; and B) see how I could use AI to make that process a bit easier. DO NOT TRUST!

Motorola MC68HC68T1P Real-Time Clock

Details

  • Location: Cabinet-3, Bin 33, Section A
  • Category: Real-Time Clock
  • Quantity: 1
  • Status: Available
  • Package: 16-pin DIP (Dual In-line Package)
  • Datasheet: MC68HC68T1 Datasheet

Description

The MC68HC68T1P is a CMOS Real-Time Clock plus RAM peripheral that contains a real-time clock/calendar, 32×8 static RAM, and a synchronous, serial, three-wire interface for communication with a microcontroller or processor. This is the DIP-16 package version of the MC68HC68T1 series.

Key Features

  • Full Clock Features: Seconds, Minutes, Hours (AM/PM), Day-of-Week, Date, Month, Year (0-99), Auto Leap Year
  • 32-Byte General Purpose RAM: Static RAM for data storage
  • Serial Interface: Direct interface to Motorola SPI and National MICROWIRE serial data ports
  • Low Power: Minimum timekeeping voltage of 2.2V
  • Burst Mode: Reading/writing successive addresses in Clock/RAM
  • Flexible Input: Selectable crystal or 50/60 Hz line input frequency
  • BCD Data Format: Clock registers utilize BCD (Binary Coded Decimal) data
  • Buffered Output: Clock output for driving CPU clock, timer, colon, or LCD backplane
  • Power Management: Power-on reset with first time-up bit
  • Freeze Circuit: Eliminates software overhead during clock read
  • Interrupt Modes: Three independent modes - Alarm, Periodic, or Power-Down
  • CPU Reset Output: Provides orderly power-up/power-down
  • Watchdog Circuit: Built-in watchdog functionality

Technical Specifications

  • Package: 16-pin DIP (0.6” width)
  • Technology: HCMOS
  • Operating Voltage: 2.2V - 5.5V (typical 5V operation)
  • Timekeeping Voltage: 2.2V minimum
  • RAM Size: 32 bytes (32×8 static RAM)
  • Interface: 3-wire synchronous serial (SPI/MICROWIRE compatible)
  • Crystal Frequency: Selectable (typically 32.768 kHz)
  • Chip Complexity: 8500 FETs or 2125 equivalent gates

Typical Pinout (DIP-16)

    MC68HC68T1P
    ┌─────────────┐
VCC │1          16│ VSS
X1  │2          15│ CE
X2  │3          14│ I/O
RST │4          13│ SCLK
IRQ │5          12│ DS
VRT │6          11│ R/W
CLK │7          10│ AS
WDI │8           9│ DS
    └─────────────┘

Note: This is a typical pinout - consult the official datasheet for exact pin assignments

Pin Descriptions

  • VCC (Pin 1): Power supply (+5V typical)
  • X1/X2 (Pins 2-3): Crystal oscillator connections (32.768 kHz typical)
  • RST (Pin 4): Reset input (active low)
  • IRQ (Pin 5): Interrupt request output
  • VRT (Pin 6): RAM/RTC backup power input
  • CLK (Pin 7): Clock output
  • WDI (Pin 8): Watchdog input
  • DS (Pin 9): Data strobe
  • AS (Pin 10): Address strobe
  • R/W (Pin 11): Read/Write control
  • DS (Pin 12): Data strobe
  • SCLK (Pin 13): Serial clock
  • I/O (Pin 14): Serial data input/output
  • CE (Pin 15): Chip enable (active low)
  • VSS (Pin 16): Ground

Applications

  • Embedded Systems: Real-time clock for microcontroller projects
  • Data Logging: Timestamping for data acquisition systems
  • Industrial Control: Time-based control and scheduling
  • Legacy System Maintenance: Replacement for vintage computer systems
  • Battery-Backed Timekeeping: Low-power clock applications

Interface Notes

  • SPI Compatible: Direct connection to SPI-enabled microcontrollers
  • MICROWIRE Compatible: Works with National Semiconductor MICROWIRE interface
  • 3-Wire Serial: Chip Enable (CE), Serial Clock (SCLK), and bidirectional Data (I/O)
  • Burst Mode: Efficient reading/writing of consecutive memory locations

Tags

rtc, real-time-clock, ram, serial-interface, motorola, dip-16, vintage cabinet-3 bin-33 section-a status-available

Notes

This is a vintage component from Motorola’s 68HC series. While discontinued, it remains useful for:

  • Restoring vintage computer systems
  • Educational projects demonstrating RTC concepts
  • Legacy system maintenance
  • Hobbyist projects requiring simple RTC functionality

The MC68HC68T1P is pin-for-pin compatible with the CDP68HC68T1 and can serve as a direct replacement. For new designs, consider modern RTC alternatives like DS1307, DS3231, or PCF8563 which offer similar functionality with better availability.

  • MC68HC68T1: Same functionality, different package options
  • CDP68HC68T1: Pin-compatible alternative
  • DS1307: Modern I2C RTC alternative
  • DS3231: High-precision I2C RTC with temperature compensation
  • PCF8563: Low-power I2C RTC alternative

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