Casio CQ-1

The Casio CQ-1 is an early attempt by Casio to combine a digital clock with a basic four-function calculator in one device. Released in 1975-1977, it has a horizontal two-piece dark brown plastic case measuring approximately 143mm x 65mm x 23-30mm and weighing 124g without batteries.

The CQ-1 is powered by a combination of batteries – two silver oxide watch batteries for the clock functions and alarms, and either one AA battery or AC adapter for the display. Battery life is estimated at 1 year for the silver oxide batteries and 10 hours for the AA.

It has an angled 8-digit blue vacuum fluorescent display for ease of desktop viewing. There are no extra digits for annunciators. The display filter has white printed text and days of the week underneath. The tiny calculator keys are long travel and squishy.

Inside are components including:

  • 1 x NEC uPD578C CPU
  • 1 x NEC uPD876C display driver IC
  • 1 x Toshiba 8-digit VFD display tube
  • 6 transistors, 11 diodes, 12 capacitors
  • 1 quartz crystal oscillator

The main CPU board sits above the keyboard and couples to it via 23 connecting wires. A small piggyback board holds voltage regulation components.

Construction involves removing plastic clips inside the case – a delicate process with risk of damage.

Logic and features:

  • Master mode switch for clock/stopwatch/calculator/set functions
  • Separate clear entry and clear all keys
  • Limits input to 8 digits, ignores overflow
  • Overflow flag ‘E’ in rightmost digit, not recoverable
  • Divide by zero gives ‘E’, not recoverable
  • Selectable constant via double press of math function
  • Minus sign indicates negative, limited to 7 digits
  • Negative zero bug: (-)(+) gives -0
  • Time/date setting not Y2K compliant
  • Multiple alarms available
  • Separate start/stop and lap keys for stopwatch

The Casio CQ-1 combines basic clock, stopwatch and calculator functionality in a compact 1970s package. However the limitations of the simple calculator design resulted in no recovery from errors and other early calculator bugs.

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