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Sharp Compet 31 (CS-31A) Desktop Calculator

Sharp Compet 31 (CS-31A)
Image Courtesy Takaharu Yoshida

The Compet 31 (Model CS-31A), announced in October of 1966 and available for sale in Japan in February of 1967, is a remake of the earlier Compet 30 Model CS-30B utilizing a small number of bipolar integrated circuits to replace discrete transistorized memory register of the Compet 30. The Compet 31 marks the first use of integrated circuits in a Japanese-made electronic calculator. From all available information(of which there is not a lot), the Compet 31 is functionally identical to the Compet 30 Model CS-30B.


Part of the Memory Circuit Board using Mitsubishi ICs in the Compet 31/CS-31A
Image Courtesy Serge Devidts

Due to patent litigation issues in the US relating to bipolar integrated circuit manufacturing processes, as well as restrictive licensing agreements for foreign manufacturers to produce bipolar ICs based on US designs, the Japanese government's Ministry of International Trade and Industry (MITI) put a moratorium on the export of any electronics from Japan that used Japanese-made integrated circuit technology, fearing that US IC manufacturers would file legal challenges against the electronic device manufacturers, as well as Japanese IC manufacturers for violation of patent rights. Because of this moratorium, Hayakawa Electric (Sharp) only sold the Compet 31 calculator in Japan, and did not export the calculator outside the country.

One thing to note on the photo above is the very clear "SHARP" stamped over the top of the manufacturer designations on the integrated circuits. Perhaps Sharp did this to make themselves responsible for their calculator if somehow it ended up outside of Japan and was discovered by MITI or worse yet, by US representatives of IC companies such as Texas Instruments or Fairchild. If this was the case, it was a pretty weak attempt, as is visible in the close-up photo below, where, even when SHARP was clearly stamped, the Mitsubishi diamond-star logo could clearly be seen, and in one case, the ink/paint that Sharp used either smeared when it was applied, or was perhaps wiped off by someone using a solvent of some type to see what was underneath the SHARP stamping. In that case, the Mitsubishi logo is again very clearly visible, as well as Mitsubishi's part number, M2340.

Giant US semiconductor manufacturer Texas Instruments was particularly picky about their IC designs, and did not want the Japanese IC manufacturers to make any chips that even had a passing resemblance to the design used by Texas Instruments (TI) to fabricate their planar-design bipolar ICs. TI was also very reluctant to grant any Japanese company license to make ICs using TI's designs, though it had granted license to Philips in the Netherlands to make chips using TI's process. It was of particular concern to Mitsubishi, who made the ICs that Hayakawa Electric (Sharp) used in the Compet 31, because Mitsubishi's legal advisors strongly advised corporate leadership that under no circumstance should a calculator with their chips in end up anywhere but in the domestic Japanese market. Mitsubishi's management was fearful of the possible ramifications, and made a formal request to Hayakawa Electric not to sell any calculator that had Mitsubishi-made chips in it outside of Japan until all of the litigation in the US had been resolved.

It isn't known if Mitsubishi's concern was only due to the threat of litigation, which would certainly make for bad publicity at the least, and would likely end up being very expensive and time consuming, and could possibly end up with them having to shut down their manufacturing lines for the ICs until any conflict was resolved; or if there were perhaps aspects of the chips that they were selling had enough of a similarity to Texas Instruments' designs that they could be considered in violation of patents even though those aspects may have been developed completely independently without any knowledge of TI's bipolar TTL chip design processes.

It should be noted here that at least one example of a calculator is known to exist in Europe with Compet 30 badging and model/serial number tag indicating it is a model CS-30B, but contains the IC-based memory board, and also has a backplane chassis with a stamping (see photo below) indicating that it has a model CS-31A. This is quite baffling, and only suppositions can be made in terms of why this particular calculator ended up this way.

There are a number of possible explanations for this oddity. One reason could be that the Compet 31 badging and model/serial number tags were not yet ready when the production line changed over to using the Compet 31 backplane and IC-based memory board. Other than the change in the backplane and the memory board, along with the badging, there is no other difference between the Compet 30 CS-30B and the Compet 31(CS-31A). If that were the case, it may be that the production line just used the existing Compet 30 badging, and the CS-30B Model/Serial number tag, continuing the serial number sequence as if the machines were Compet CS-30Bs. Once the badging and model/serial number tags stating Compet 31/CS-31A were ready, the line started using them. Another possibility is that this might have an attempt by Sharp to get by MITI's moratorium on the export of IC-based devices by disguising IC-based machines with the existing model number of calculators that did not have integrated circuits in them. The Compet 30 Model CS-30B was entirely made of discrete components and thus would not have fallen within MITI's export ban. This trick may have been used to allow the sale of Compet 31's, which were priced $200 less at retail than the CS-30B due to the reduction in cost associated with the use of integrated circuits. This may have allowed Sharp to export the calculators and sell them at an ever better competitive price outside of Japan than other competitors, generating extra revenue that otherwise wouldn't be available. At the time, 70% of Sharp's calculator revenue came from export products. It this was the case, it was a rather sneaky, but clever way to skirt the export ban put in place by the Japanese government.

The CS-31A uses 28 small-scale bipolar integrated circuits made by one of the earliest Japanese integrated circuit manufacturers, Mitsubishi. The devices, which have part number M2340, are in plastic dual-inline packages, and are fabricated with TTL (Transistor-Transistor Logic) construction. Each package contains four two-input NAND gates, very similar to the first of Texas Instruments' famous 7400-series TTL ICs, the SN7400. Only the memory circuit board of the thirteen circuit boards in the Compet 31 uses integrated circuits, with the rest of the boards utilizing the same discrete transistor construction as in the Compet 30. The logic gates in the ICs are connected in such a way that they create flip flops that take the place of the transistor-based flip flops that make up the memory register in the Compet 30, significantly reducing the component count and complexity of this board as well as reducing the retail price of the calculator by approximately $200US.


Stamping in Model CS-30B Calculator Backplane indicating Model CS-31A Backplane Assembly
Image Courtesy Serge Devidts

It is suspected that very early Sharp Compet 31 (Model CS-31A) calculators may have been badged as Compet 30 calculators with Model CS-30B Model/Serial Number tags, but used the IC-based memory board and CS-31A backplane, because the production versions of the badging for the Compet 31 were not yet ready. It is assumed that the manufacturing line had already been switched over to manufacturing the Compet 31 memory board and backplane, and rather than hold up manufacturing of the Compet 31 because of the lack of badging, the Compet 30 badging was used, since both the Compet 31 and the Compet 30/CS-30B functioned identically, and from a user perspective, were indistinguishable from each other. Once the production Compet 31 badging was ready, the line began using the Compet 31 badge, and placing Compet 31/CS-31A Model/Serial number tags on the machines coming off the line. This is only supposition at this point, because as of this writing, no known examples of a Compet 31-badged calculator have been found. If you are reading this, and know of the existence of a Sharp Compet 31 calculator, with the "Compet 31" badge and model number of CS-31A, please EMail the Old Calculator Museum and let us know about it.

The Compet 31 marked the beginning of the proliferation of integrated circuit technology in Sharp's electronic calculators. The next model in the series, the Compet 32, introduced not long after the Compet 31, marked a new generation of calculators for Sharp, used a completely different architecture than Sharp's earlier electronic calculators. The Compet 32 switched to use of a bit-serial (rather than digit-parallel) mode of operation, multiplexed display system, and adopted the use of a small magnetic core memory for storage of the working registers. These changes drastically reduced the complexity of the Compet 32 as compared to the earlier machines, substantially shrinking the calculators in size and weight, as well as increasing reliability and decreasing production and sales price. Along with the architectural changes, the same Mitsubishi M2340 ICs as used in the Compet 31 were used in the Compet 32, this time as state storage flip flops since the magnetic core served to store all of the working registers of the calculator, including the memory register. Successive models of Sharp calculators increased the number of integrated circuits used, at first continuing the use of bipolar ICs, then rapidly switching over Japanese-made small and medium-scale Metal-Oxide Semiconductor (MOS) integrated circuits of ever-increasing complexity as Japanese IC manufacturers NEC and Hitachi perfected their MOS IC processes. Sharp was the first Japanese electronic calculator company to leverage domestically-made ICs in their calculators, and it was this move that gave them a distinct competitive advantage over other Japanese calculator manufacturers that relied on discrete transistor designs, or more expensive bipolar integrated circuits imported from US (Signetics/Philco) or European (Philips) IC manufacturers.

If you own or know of a Sharp Compet 31 calculator, please press the EMail button at the top of the page, and send an EMail about the calculator. Even if it isn't available for the Old Calculator Museum to acquire, information you can provide could be very helpful in adding to the story of the Compet 31.


Sharp Compet 31 (CS-31A) Specifications

Manufacturer: Hayakawa Electric Co., Ltd. (Sharp)
Model Number: CS-31A (Compet 31)
Manufactured In: Japan
Date of Introduction: October, 1966
Display Technology: Nixie Tube, 14 Digits
Logic Technology: 28 Small-Scale bipolar(TTL) Mitsubishi M2340 ICs, 553 Transistors, 1,549 Diodes
Math Functions: Four Function
Digits of Capacity: 14
Decimal Modes: Fixed via keyboard pushbuttons
Settable at 0, 2, 4 or 6 digits behind decimal
Push-on/Push-off Round-Off Mode, [R] key
Memories: One accumulator-style memory register implemented with Integrated Circuits
Constant: Automatic on Multiply & Divide
Size: 17 1/4" wide, 18 3/4" deep, 8 1/2" high
Performance (Manufacturer Claimed): Addition/Subtraction: 15ms
Multiplication: 150ms
Division: 190ms

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