Texas Instruments TI-3000
The TI-3000, along with a slightly more capable machine, the TI-3500, were TI's first forays into the frenetic desktop electronic calculator market of the early 1970's. With TI's development of a variable function (through mask programming) single-chip calculator LSI, it was possible for TI to compete in the extremely competitive market of the time due to the simplicity of manufacturing the machines. Because of this chip breakthrough, TI was able to get a jump on some of the other calculator manufacturers of the time that had to settle with multi-chip implementations, which were more complex, and thus more expensive to manufacture. Texas Instruments stamped out tens-of-thousands, if not more, of the 3000 beginning in the fall of 1972 and extending through sometime in 1974. These calculators were extremely popular in High School and College math and science departments...making it one of the first electronic calculators to be deployed in large numbers in the school system, replacing the aging electromechanical calculators that so many institutions had invested their funding into during the 1950's and '60's.
The Back side of the Circuit Board
On a personal note, I used one of these quite a bit in my Jr. High science classes, and when I saw this particular machine available, it brought a lot of memories. A friend and I used to tinker with one of these calculators in electronics class. We figured out where the clock generation circuitry was. By adding in a variable resistor, we were able to vary the clock rate. The machine didn't take well to increasing the speed of the clock, but it worked great with the clock slowed down, and it was very educational to watch it carry out operations with the clock running at a slower rate. At one point I remember we had the clock running so slow that it would take about 1/2 second for a keypress to even register on the display.
The TI-3000 without the top cover
A slight historical diversion is appropriate before delving into the operational details of the TI-3000. The 3000 is somewhat historical, as it was TI's first desktop calculator product, as well as utilizing TI's own first series of single-chip calculator IC's. The TMS0100-series of calculator chips were made publically available by TI in September of 1971, though they were being sold to customers such Heathkit (see the Heathkit IC 2008A exhibit) under inside purchasing agreements as soon as early 1971. The TMS0100-series of IC's all share essentially the same general logic, designed in part by one of TI's calculator gurus, Michael J. Cochran. Mr. Cochran originally got started in the calculator design business in the late 1960's, working for Cintra (see the exhibit on the Cintra/Tektronix 909 for an example of Mr. Cochran's work at Cintra). Sometime in 1970, Mr. Cochran left Cintra and went to work for Texas Instruments, and became one of TI's most valuable calculator architects. Later developments of Mr. Cochran include the amazing SR-60, as well as many other contributions that set the stage for Texas Instruments to still be a player in the electronic calculator business today.
The TI-3000 is based on a TMS0109 IC, which is one of the masked-programmed variants of the TMS0100-series of single chip calculator IC's. The difference in the various individual part numbers in the TMS0100-series lies in the content of programming inside the chip, done via via masks used in the IC manufacturing process to preset the content of ROM and Programmable Logic Arrays (PLA) to provide a given selection of functionality. Using this method, things such as the number of digits of capacity, display rendition, decimal point handling, roundoff, and other features could be implemented with relative ease.
The TI-3000 is a basic eight digit, four function calculator. It uses a Burroughs Panaplex II display, with nine digit positions. The left-most digit position is used only for sign and error indication. Erroneous calculations, such as dividing by zero, result in an "E" showing up in this position, and overflows result in an "o". Either error condition locks the keyboard until the [C] key is pressed to clear the machine. The [CE] key is used to clear the entry register, allowing for correction of erroneously entered numbers. The machine operates very conventionally, with arithmetic logic. The [+=] and [-=] keys are used for addition and subtraction, and the [+=] key is also used to terminate multiplication and division problems. The 3000 provides automatic floating decimal point placement.
The TMS0109 'calculator on a chip'
The machine uses a sealed keyboard assembly which utilizes a conductive pad on the bottom of the key stalk, which make contact with traces on the circuit board below the keys, closing the circuit. This design led to "bouncy" and intermittent keys on machines which were subject to dusty environments. Fortunately, the exhibited machine seems to have been kept in a relatively clean environment, and the keyboard works great.
Detail of the 9-digit Burroughs Panaplex II Display Module
The calculator uses discrete transistor circuitry to drive the multiplexed display panel. As I mentioned before when in Jr. High School, a friend and I played around with varying the clock rate of the machine. By varying the resistance in the clock generating circuitry, we were able to get the machine running slow enough that the multiplexing of the display was plainly visible. A single TTL 7400-series (7406) IC accompanies the LSI calculator chip, and appears to be used as part of the clock generation circuity. The date codes on various components within the machine place the exhibited unit as having been produced in early 1973.
A Close-Up of the Panaplex Display in Operation
The 3000 calculates pretty quickly, with 'all nines' divided by one taking just over a blink of an eye to complete.