IBM PS/2 P70 (Late)

Chipset parts: IBM 90X8134 (DMA) IBM 33F5946 (CPU Gate Array) IBM 33F5838 (I/O Gate Array) IBM 33F5944 (Memory Controller) IBM 57X4111 Motorola MC146818AP (Real-Time Clock + RAM)

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Release date:  1990-03-20      [see all boards with this chipset]


This chipset is found on the late P70 motherboard. It operates and 16 or 20MHz. It is very similar to the model 70 type 2 chipset.

90X8134 DMA

No datasheet exists for this chip. Sometimes labeled 90X8134ESD

33F5946 CPU Gate Array

No datasheet exists for this chip. It is a gate array that is connected to the CPU. It is also marked NEC, though programmed (at the factory) by IBM. It only exists on the model 70 type 2 and late P70 motherboards.

33F5838 I/O Gate Array

This chip has no datasheet. It is only found on the model 70 type 2 motherboard and the late P70 motherboard. It is some type of gate array, that on the P70 is connected to I/O.

33F5944 Memory Controller

No datasheet exists for this chipset. It is is only found on the model 70 type 2 and late P70 motherboards. It is likely a gate array manufactured by NEC and programed (at the factory) by IBM.


This part is also labeled MS700CD on the model 80 type 3 motherboard. or MS700 on the P70 late motherboard. It is also found on the model 70 T1. T2 and T3. Conjecture: It is likely a gate array configured as perhaps a MCA interface. There has not been further investigation.

Motorola MC146818A Real-Time Clock + RAM:


  • MC146818P - plastic DIP
  • MC146818C - plastic DIP extended temp range.


  • MC146818A? - QFP (Datasheet states it is available, no p/n)
  • MC146818AC - plastic DIP extended temp range.
  • MC146818AL - ceramic DIP
  • MC146818AP - plastic DIP
  • MC146818AS - CERDIP
  • MC146818AF - SOP
  • MC146818AFN - PLCC

The A variant is newer. It has two additional pins, 1 and 16 that are NC on the non-A. Pin 1 is MOTEL, Tying it high or low determines if the chip uses Motorola or competitor e.g. Intel timing. Pin 16 is Standby. This was previously handled by the chip enable pin in the non-A. Details can be found on page 11 of both datasheets.

The MC146818A Real-Time Clock plus RAM is a peripheral device which includes the unique MOTEL concept for use with various microprocessors, microcomputers, and larger computers. This part combines three unique features: a complete time-of-day clock with alarm and one hundred year calendar, a programmable periodic interrupt and square-wave generator, and 50 bytes of low-power static RAM. The MC146818AFN uses high-speed CMOS technology to interface with 1MHz processor busses, while consuming very little power.

The Real-Time Clock plus RAM has two distinct uses. First, it is designed as a battery powered CMOS part (in an otherwise NMOS/TTL system) including all the common battery backed-up functions such as RAM, time, and calendar. Secondly, the MC146818A may be used with a CMOS microprocessor to relieve the software of the timekeeping workload and to extend the available RAM of an MPU such as the MC146805E2


  • Low-Power, High-Speed, High-Density CMOS
  • Internal Time Base and Oscillator
  • Counts Seconds, Minutes, and Hours of the Day
  • Counts Days of the Week, Date, Month, and Year
  • 3 V to 6 V Operation
  • Time Base Input Options: 4.194304 MHz, 1.048576 MHz, or 32,768 kHz
  • Time Base Oscillator for Parallel Resonant Crystals
  • 40 to 200 uW Typical Operating Power at Low Frequency Time Base
  • 4.0 to 20 mW Typical Operating Power at High Frequency Time Base
  • Binary or BCD Representation of Time, Calendar, and Alarm
  • 12- or 24-Hour Clock with AM and PM in 12-Hour Mode
  • Daylight Savings Time Option
  • Automatic End of Month Recognition
  • Automatic Leap Year Compensation
  • Microprocessor Bus Compatible
  • Selectable Between Motorola and Competitor Bus Timing
  • Multiplexed Bus for Pin Efficiency
  • Interfaced with Software as 64 RAM Locations
  • 14 Bytes of Clock and Control Registers
  • 50 Bytes of General Purpose RAM
  • Status Bit Indicates Data Integrity
  • Bus Compatible Interrupt Signals (IRQ)
  • Three Interrupts are Separately Software Maskable and Testable
    • Time-of-Day Alarm, Once-per-Second to Once-per-Day
    • Periodic Rates from 30.5 us to 500 ms
    • End-of-Clock Update Cycle
  • Programmable Square-Wave Output Signal
  • Clock Output May Be Used as Microprocessor Clock Input
    • At Time Base Frequency /1 or /4
Drivers: not available
Documentation: 1 file
Other files: not available