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Commodore US*14

This calculator bears a strong resemblance to a another calculator in the museum, the Panasonic 1000. The resemblance seems more than conicidental, and it is, because Commodore had an OEM relationship with Panasonic (Matshushita) that began sometime in the late 1960's to early 1970's. That explains why there are so many similarities in designs of calculators from the two vendors. The Panasonic 1000 is a slightly earlier calculator, being made in 1971, and using less-complex Large Scale Integrated circuits. This US*14 was made in the late part of 1972, and benefits from advances in integrated circuit technology, trimming the IC count, and expanding the functionality of the machine. It appears that the US*14 was introduced as early as late 1971.

The US*14 is yet another in a fairly long line of "US*" calculators sold by Commodore. Other calculators in the museum in this line include the US*1, US*8, and the US*10. All of the US* line of calcuators were designed to be inexpensive, making the price of entry into the world of electronic calculators less of a barrier for consumers to consider for use in the home. The US*14 had an introduction price of $159.95, putting it within the means of mid to upper-income consumers of the time.

View of the Sperry Gas-Discharge Display in Operation

The US*14 uses a somewhat unusual display technology, consisting of a number of Sperry-made multi-digit (one three-digit, and six two-digit) modules, for a total of fifteen digit positions. The Sperry display modules are similar in operation and design to the Burroughs Panaplex display panels, however, rather than having a whole display panel integrated into one module, the Sperry modules come in groups of two or three digits, allowing creation of displays with anywhere from two digits on up.

The Display Circuit Board

The Sperry display modules are designed so that they can be butted up next to each other, maintaining the digit spacing. The display modules are all soldered to a circuit board which plugs into an edge connector mounted on the main circuit board. The display modules use the standard seven-segment digit rendition, with a triangular shaped decimal point to the lower right of each digit. The same display technology is used in the Tektronix 31 calculator exhibited here, as well as in a kit calculator (albeit in the next larger digit size), the Heathkit 2008-A. The right-most digit of the display is used as a status indicator. A negative number is indicated by lighting the bottom most horizontal segment of the status digit. The upper three segments of the status digit light up when the memory register has been accessed using the "M+" or "M-" keys, and the status digit shows "E" when the calculator has detected an overflow or error condition.

US*14 Keboard Detail

The US*14 provides the standard four math functions, along with a percent calculation. It has a single memory accumulator, with "M+" and "M-" keys to add/subtract the content of the display from the memory accumulator. The "RM" key recalls the content of the memory register to the display, and the "CM" key clears the memory register. The memory status indication mentioned above operates differently than most. Most memory status indicators are lit anytime the memory register contains a non-zero value. Not so with the US*14. A depression of the "M+" or "M-" keys lights the indicator, even if the memory register contains zero as a result of the operation. Pressing the "CM" key clears the memory status indicator. It appears that rather than check the memory register for zero content, the memory status indicator of the US*14 is simply a latch that is set by the operation of the "M+" or "M-" keys, and cleared by the "CM" key. A push-on/push-off "sigma" key allows results of multiplications or divisions to automatically be accumulated in the memory register.

The US*14 operates in fixed or floating decimal as selected by a thumbwheel selector at the left of the keyboard panel. Fixed decimal point operation can be selected by dialing in zero through seven digits behind the decimal point. Two positions of the thumbwheel switch contain an "F" setting, which selects floating decimal operation. The machine provides leading zero suppression, and when in floating decimal mode, it always right-justifies the display so that any trailing zeroes are eliminated. A round-off mode switch is located next to the decimal mode thumbwheel, that provides settings for force up, 5-up/4-down rounding, and force down (truncate) modes. The percentage function operates as an "=" key, terminating multiplication and division operations, for example to find 25% of 16, one would enter "16 X 25 %" and the display would show 4. The "K" key, a push-on/push off switch, provides for constant calculations, and operates for mulitplication and division operations.

Error detection on the US*14 is unusual, with error and overflow being reliably detected and indicated, however, the machine does not 'lock' when such a condition exists. The right-most digit position in the display shows an "E" when an error or overflow occurs, but the machine will merrily continue calculations. Pressing the "C" (Clear All) key extinguishes the error indication. The "E" indication will also occur if the memory register overflows. The "CI" key clears the display for use in correcting input errors. The "EX" key exchanges to order of operands for multiplication and division operations.

Inside the US*14

The US*14 is one of the few low-cost calculators that was manufactured in North America at the time. By the early 1970's, the Japanese had pretty much claimed the market for manufacture of low-cost calculators. Most of the calculator manufacturers that still made their machines in North America were focusing on high-end calculators. Manufacturers like Hewlett Packard, Computer Design Corporation (Compucorp), and Wang made their calculators in the US, but these were machines that cost thousands of dollars and offered much more complex functionality than most of the Japanese calculators. In this high-end market, the price sensitivity wasn't as critical as it was in the low-end market, which allowed the North American manufacturers, with their higher labor costs, to market their machines successfully against the flood of low-cost calculators from Japan. It seems odd that the US*14, targeted as a low-cost machine, didn't end up being made overseas.

In spite of its low-cost, the US*14 is a nicely built machine. The calculator's guts are all contained on one main circuit board, a very high quality fiberglass circuit board. The circuit board is single-sided, with wire-jumpers making connections on the component side. Very legible silkscreened component identifications are printed on the circuit board, making it much easier for repair technicians to identify the correct part when doing service. The weakest part of the design of the US* line of calculators is the keyboards. The keyboards use spring-type contacts in sealed modules. For whatever reason, gunk tends to get inside the switch module, gumming up the works, and causing intermittent keyswitch operation. Every Commodore US*-series machine in the museum has had keyboard problems which required remedial efforts to fix.

The Main Circuit Board of the US*14

The US*14 uses a very unusual three-chip LSI chipset that was designed by a firm called IST, which stood for Integrated Semiconductor Technology. IST was an integrated circuit design firm that would design full-custon integrated circuits for anyone who had a design that they wanted implemented in integrated circuit form. IST did not manufacture IC's -- they only designed them. he manufacture of the ICs was farmed out to various IC manufacturers once the design and photo-artwork were completed by IST.

The story of IST is rather interesting, because it is a keen illustration of how the threads of technological history have unique ways of entangling. IST was founded in 1968, by a number of folks who left Philco-Ford Microelectronics to start the custom IC design firm. These highly skilled people left Philco-Ford, because earlier, in 1966, Philco-Ford had purchased an early MOS Integrated Circuit design/manufacturing company called General Micro-electronics. General Micro-electronics was formed as a spionff of folks who left Fairchild Semiconductor to pursue the belief that Metal Oxide Semiconductor (MOS) integrated circuitry was the wave of the future. GM-e holds a significant place in electronics history, as the company developed the first implementation of the digital logic of an electronic calculator in a MOS IC chipset. This development was done by GM-e under contract to Victor Comptometer, who ended up marketing the world's first Large-Scale Integration electronic calculator, the Victor 3900 (see the exhibit on the Victor 14-322 for more information on the Victor 3900), in October of 1965 - almost three years before this level of integration appeared in any other calculator.

The chipset used in the US*14 consists of two 16-pin, and one 18-pin package. The part numbers are 7061, 7062, and 7063. The packages are ceramic dual-in-line, with gold plated pins. The LSI's are plugged into sockets of the like I've not seen before, similar to Molex strips.

Closeup of the "IST"-made LSI IC Chipset

Along with the three LSI's, there is a sprinkling of six TTL 7400-series devices that provide various glue functions. Among these, a 7442 (a fairly rare IC today) is used to convert the Binary Coded Decimal (BCD) output of the calculator chips to seven-segment form for the display. Two more IC's, made by Sperry (DD-700), are specialized chips for driving the Sperry gas-discharge display modules. Date codes on all of the chips range from mid-1972 to late-1972. Along with the IC's, the machine has a surprising number of discrete transistors. Some are used in the power supply section, others appear to be related to clock generation, and lastly, some are used in the display driving circuitry.

The US*14 is about average in speed for a 14-digit calculator, with the all-nines divided by 1 problem taking about 1/3 second. During calculation, the display is blanked.

Text and images Copyright ©1997-2011, Rick Bensene.