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(Not Any More)
Sharp Compet 32 Desktop Calculator
The Old Calculator Museum has acquired a physically very nice Sharp Compet
32 calcualtor that required some electronic repairs. The electronic
issues, one with the power supply, and another issue with a bad
transistor and diode in the display system, have been diagnosed and
repaired. The exhibit for the calculator (pictured above) is in the process of
being prepared. Check the Old Calculator Museum's
Change Log periodically
for a note indicating the posting of the online exhibit for the Compet 32.
The Sharp Compet 32 is a sea-change for Sharp's electronic calculator
architecture. Prior generations of Sharp's electronic calculators
utilized an architecture whereby the working registers of the calculator were
implemented with discrete transistor flip-flops arranged as shift
registers, and a digit-parallel scheme for the arithmetic unit, meaning
that mathematics were performed a decimal digit (4-bit Binary Coded
Decimal) at a time, with separate decoder-drivers for each digit in
the display, requiring a large number of components, including 10 transistors,
a bunch of diodes, as well as a number of resistors, for each digit in the
display. The Compet 32 switched this up by adopting a bit-serial architecture
by which all processing was done a single bit at a time, with a serial
arithmetic logic unit that handled bit-at-a-time Binary Coded Decimal
arithmetic. This bit-serial architecture allowed for "time shared" drive
of the Nixie tube display, with only one decode-driver arrangement for
all of the tubes, with each tube lit with its content for a short period
of time, with the digits scanned sequentially at fast enough rate that the
human eye perceives the display as continuous. The Compet 32 also adopted
a small magnetic core memory array to store the working registers of
the machine, drastically reducing the component count versus the discrete
transistor flip flop shift registers of the earlier calculators.
Last, but not least, the Compet 32 utlized a small number of Mitsubishi-made
bipolar Transistor-Transistor-Logic (TTL) integrated circuits to implement
varous state flip-flops in the control circuitry of the machine, again,
reducing the component count. The Compet 32 still used a great many
discrete transistors and diodes for the majority of its logic, but the use
of these ICs, though not Sharp's first use of Integrated Circuits, marked
the beginning of Sharp's transition toward much more comprehensive use
of integrated circuits in its future calculators.