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Friden/Singer EC-1113 Calculator

Updated 2/2/2019

The Friden/Singer EC-1113 is a basic 12-digit four-function office calculator with a single accumulator-style memory register, utilizing a Nixie tube display. The EC-1113 was designed and manufactured for Friden by Hitachi, Ltd. in Tokyo, Japan, under an agreement forged between the companies for Friden to sell the Hitachi-made machines within its market under the Friden brand name. It's not known exactly when this agreement was made, though it's likely it occurred sometime during the 1967 to 1968 time-frame.

As part of the 1965 Singer buyout of Friden, Singer's management began to realize that it was no longer cost-effective for Friden to continue to design and manufacture electronic calculators in the US. The Japanese had become very adept at design and manufacture of electronic calculators that were significantly less-expensive due to low labor costs and a favorable exchange rate. Friden's new management first tested the market on a somewhat limited scale sometime in the latter part of 1967 by importing and marketing a transistorized electronic calculator designed and manufactured by Hitachi, the Friden 1112. Hitachi's version of the machine, the ELCA-12, was Hitachi's first production electronic calculator. The reasonable success and solid profit margin of the Friden 1112 made it clear that more money could be made by Friden marketing and supporting calculators designed and manufactured in Japan. At that point, Friden's management began slowly dismantling its US-based calculator engineering and manufacturing operations in favor of OEM agreements with Hitachi, and later, other off-shore calculator manufacturers. Singer re-focused the Friden division on the development of electronic billing machines, and later, small to medium-scale computer systems.

The Hitachi version of the Friden EC-1113 was known as the ELCA-22, and was sold successfully in Hitachi's domestic market. The ELCA-22 was Hitachi's first integrated circuit based calculator, utilizing Hitachi's own first-generation PMOS small-scale integrated circuits. These integrated circuit devices were among the earliest MOS IC's produced in volume in Japan. The ELCA-22 was introduced in Japan in July of 1967. The EC-1113 was introduced by Friden in February of 1969, providing an indication that the agreement for Friden to become an OEM customer of Hitachi occurred sometime before then. The EC-1113 predates its stable-mate machines, the Singer/Friden 1114 and Singer/Friden 1115, which are machines of very similar appearance, function and mechanical design, but were made with newer technology integrated circuits. Note that the exhibited calculator has a "Friden" nameplate on the keyboard panel versus the Singer legend on the later machines. This machine was built during a time when Singer had not yet completely switched all Friden products to be badged "Singer/Friden Division". The EC-1113 was the first of a long line of Hitachi-designed and manufactured electronic calculators imported by Friden and sold and supported under the Singer/Friden badge.

The Friden EC-1113 Opened Up

The 1113 is built from five circuit boards that plug into a hand-wired backplane. The boards stack horizontally inside the machine, arranged in a stamped sheet-metal cage that provides shock isolation and stability for the cards. The top circuit board in the stack is smaller than the other boards and provides power supply regulation and filtering functions, as well as containing the master clock oscillator and keyboard input conditioning circuitry. The second board contains the display decoding and driving circuits, including the twelve Hitachi-made CD-79 Nixie tubes and associated driver circuitry. Early versions of the EC-1113 used Hitachi's CD-71 tubes, which were superseded by the CD-79's shortly after introduction. The third board contains the arithmetic unit, along with the accumulator and memory register logic. The fourth board makes up the master control and sequencing logic. The bottom-most circuit card provides the timing chain, as well as the display register storage.

Close-up View of Hitachi HD701 Dual 8-Bit Shift Register Integrated Circuit

The EC-1113 uses a total of 108 first generation Hitachi HD7xx-series PMOS integrated circuits in metal can packages, with each device having 12 pins. The full complement of devices used in the machine is (with the number devices of each type listed in parenthesis after the part number): HD701 Twin 8-bit Shift Registers (9), HD703 Quad Inverters (17), HD704 Dual 4-In AND Gates (9), HD705 Dual JK Flip Flops (20), HD707 Quad D-Type Flip Flops(5), and HD712 Dual 2-In AND Gates & Single 3-In AND Gate (48).

The Circuit Boards of the EC-1113

The EC-1113 differs from its later brothers in the EC111X-series of machines by virtue of the fact that it operates with full floating decimal point. The later machines in the series all operate with fixed decimal point positioning.

A Closer View of the EC-1113 IC's

There are some quirks with the operation of the machine are not faults with the circuitry, but rather are by design to simplify the logic of the machine. The machine does not generate a correct result on division problems which have a dividend greater than eleven digits (including digits behind the decimal point). Performing such calculations results in incorrect answers and false overflow conditions. Multiplications that result in products which have more than eleven digits give incorrect answers and false overflow indications. The reason for this behavior is that one digit of the machine's working register is consumed by a special "marker" digit, which consists of all four bits encoding the digit being a '1' (e.g., 1111 in binary). This marker is used by the logic to determine when the multiplication or division operation is complete. As a result, one digit of the machine's capacity is "lost" due to this design, causing the unexpected results. The EC-1113 also appears to have rather poor power-on initialization. Many times when first powered up, the display will contain gibberish, with multiple digits lit up at once within a Nixie tube, multiple decimal points on at once, and sometimes the machine will be locked due to a spurious overflow condition. The memory register can also come up with random and sometimes invalid content. Pressing [C] followed by [CM] after powering up assures that this random content is cleared out, and the machine ready for use. If this isn't done, the random content of the registers of the calculator can lead to strange behavior of the machine until it is cleared properly.

Detailed View of one of the EC-1113 Circuit Boards

The memory functions operate as expected, with [M+], [M-], memory recall ([RM]), and memory clear keys ([CM]). A push-on/push-off [∑] key allows for sums of products(multiplication) to automatically accumulate in the memory register. The 1113 lacks a "Clear Entry" key, opting instead for a [←] key that allows entered digits to be erased digit at a time. This is an unusual feature, and may be the only Friden calculator that has this function -- all of the other 111x-Series machines opt for a "Clear Entry" function to allow the user to correct mistaken input.

A View Showing the Hitachi CD79 Nixie Tube Nomenclature

As noted earlier, there are two different versions of the EC-1113 (and likely the Hitachi version of the machine). The earlier version of the EC-1113 uses Hitachi CD-71 Nixie tubes. At some point fairly early in the manufacturing lifetime of the machine, an engineering change was made to utilize Hitachi CD-79 Nixie tubes rather than the CD-71 devices. There are specialized transistors used on the Nixie display circuit board (marked with a black dot on top of the transistor case) that are specially selected to properly match the characteristics of the CD-71 tubes. The revised version of the Nixie display board replaced the CD-71 Nixie tubes with CD-79 devices, which have different characteristics that no longer required specially selected cathode drive transistors. This change reduced costs and improved the reliability of the display system.

A neon indicator at the left end of the display indicates overflow condition. When an overflow occurs, this indicator lights, and keyboard input is ignored until the calculator is cleared using the [C] key. A similar indicator on the right end of the display lights to indicate that the number in the display is negative.

The EC-1113 operates at a master clock frequency of approximately 42KHz. The early Hitachi integrated circuits used in the calculator are not tremendously fast devices, and thus a conservative clocking rate was used to assure reliability rather than raw speed. This makes the EC-1113 measurably slower than its successors in the 111x line of machines, as Japanese MOS integrated circuit technology continuously improved over time. Hitachi claims that the average addition or subtraction takes 40 milliseconds(mS), or 0.04 seconds; multiplication, 73mS; and division, 80mS. For "worst-case" observed figures, the EC-1113 takes about one second to calculate the quotient of eleven 9's (the largest allowable divisor) divided by one. Multiplication of 99999 by 99999 takes about 1/2 second (500mS).

Text and images Copyright ©1997-2023, Rick Bensene.

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