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SCM Cogito 414 Desktop Calculator

Updated 11/3/2023

The SCM (Smith Corona Marchant) Cogito 414 is the first calculator offered by SCM to be implemented fully with large-scale integration (LSI) Metal-Oxide Semiconductor (MOS) integrated circuits. Shortly after the 414 was introduced on April 23, 1968, a virtually identical calculator, the Cogito 412 was introduced, with the sole difference being in the number of digits of capacity -- 14 for the Cogito 414, and, twelve for the Cogito 412. In terms of function and operation, the machines are identical. The same main circuit board is used in both machines, though different IC's are used in the 414 versus the 412 due to the extra two digits of capacity on the 414. An article in the New York Times dated April 24, 1969, announces the Cogito 414, touting its use of Large Scale IC technology as enabling it to be the smallest machine on the market with full calculator functionality.

A Look at the Display Board & Driver Circuitry

It is estimated that the exhibited Cogito 414 was built in the early 1970 time frame, with date codes all but one of the IC's in late-1969, and a single IC with a 1972 date code . The IC with the '72 date code is suspected to be a service replacement, since all of the other IC's as well as a few other components are dated in mid-to-late 1969. In cases where there is a single or a few outliers in the date codes, it's fairly safe to assume that date code range of the earliest ICs in the machine give the closest base upon which a build date can be extrapolated. In the exhibited Cogito 414, the IC with the 1972 date code is located on the main board. All of the IC's on the main board are plugged into Molex-style sockets, so the chips are easily replaced without any evidence left of the replacement. Soldered-in chips leave signs of manual soldering of a replacement chip which can be solid give-away that a device has been replaced. IC's installed in sockets don't leave such traces of replacement.

SCM Cogito 414 Internal View

The eight MOS-LSI arrays in the Cogito 414 consist of two read-only memory (ROM) arrays that contain microcode that provides low-level instructions that are used to create the functionality of the calculator. Another chip contains three 68-bit shift registers that make up the working registers of the calculator. Another MOS array consists of a serial-in/serial-out digit parallel BCD adder that also contains a four-bit (single digit) delay and carry storage flip-flops. A keyboard processing array that de-bounces and encodes key-presses and stores the key-code in a register that is accessible by the other chips to identify the key that has been pressed. There is also a data flow chip that selects a register in the registers chip and routes serial bits from the register to the adder and back to a selected register in the register chip. There is also a chip that generates the master timing signals to synchronize the operation of all of the other chips. Last but not least, a chip that contains the display logic, including a four bit shift register that stores the digit to be displayed, a BCD to 1-of-10 decoder selecting the numeral in a Nixie tube to light up, and multiplexing logic to select the digit position to be lit, along with decimal point display logic. The eight chips are all interconnected with each other to provide the complete functionality of the calculator. There are very few discrete components in the Cogito 414 as a result of the high level of implementation of the calculator functions into the eight LSI chips, which were designed collaboratively between SCM and American Micro-systems Inc. (AMI) in a two and a half year-long effort. Once the design was complete and verified, AMI provided manufacture of the ICs exclusively for SCM.

Cogito 412/414 Keyboard Detail

Internally the 414 differs a bit from the 412. The 412 uses two daughter boards, each with two LSI IC's soldered onto them that plug into edge card connectors on the main board. The Cogito 414 combines the two daughter boards into one, with four LSI's on it, but the IC's on the 414's daughter board are different than those on the 412. It is suspected that the IC's on the motherboard provide the core functions of the machine, including the timing chip, the adder, the data routing chip, and the register chip. These ICs are universal in function, and are common functions in virtually any electronic calculator, thus they are easily shared between models of calculators with varying features and functions. This allows the main board to be used in different models of calculator, while the daughter board or boards contain the ICs that vary between models, giving them their individualized functionality. These plug-in boards would be home for the ROM chips, the display chip, and the keyboard chip. This is just a theory, but it would make sense from the standpoint of providing economy of scale by providing for use of the motherboard in different models of calculator, with the plug-in board(s) providing the unique functionality/feature aspects of the specific models. This is further substantiated by the fact that the chips on the motherboard have the same part numbers in the Cogito 412 and Cogoto 414, while the daughter card ICs have different part numbers.

Back View with Display Driver Detail

The 414 is only barely detectably slower by human observation than the 412, likely due to the extra two digits of calculating that has to occur on each calculation. 9999999999999.9 divided by 1 takes just a shade over 1/2 second to complete.

For more details about the Cogito 414, please refer to the exhibit for the >SCM Cogito 412. To see an original ad (scanned black and white to save on image download time), click HERE.

Text and images Copyright ©1997-2024, Rick Bensene.
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