Commodore C112 Calculator, TESTED GOOD, Circa 1971

Appearance: UsedFunctionality:WorkingDescription:============As pictured, a CommodoreC112 Calculator – tested good. Original power cord was lost, but an adapted oneis included.About Us:=========The ComputerPreservation Group is dedicated to the preservation of historical computers. Tohelp fund ongoing operations, select items are made available. To learn more,please visit our website: www.computerpreservation.com. Thank you for your support!Warranty andReturns:=====================We understand thatthere may be compatibility issues, space constraints, or it just doesn’t lookperfect. This item can be returned within 14-days for ANY reason. However,shipping to and from is not refundable. Shipping:=========- Local pickup isalso available at no cost.- Most orders placedbefore 9am will ship the same day.Stock#:5551Details from http://www.oldcalculatormuseum.com/commc112.html:The Commodore C112is an early Vacuum- Fluorescent (VF) display electronic calculator, made in themid-to-late 1971 timeframe. It uses rather unusual individual VF display tubes,made by Futaba, each of which have ten segments to form the digits, along witha decimal point, and a 'comma' (which isn't used in this application). Theresulting digits have more fully-formed looking digits than more conventionalseven segment displays, but aren't quite as unique as the Itron displayelements in the Sharp EL-160. This calculatorwasn't really made by Commodore. In fact, it was actually manufactured byUnicom, a business unit of integrated circuit manufacturer AmericanMicrosystems, Inc. (AMI). AMI formed Unicom as an outlet to market calculatorsbased on AMI's early MOS/LSI calculator chipsets. AMI sold a number ofdifferent calculators under the Unicom brand name, as well as selling to anumber of OEM customers, including Commodore in Canada, and Ricoh in Japan.Unicom was sold to Rockwell International in 1972. For a time, Rockwellcontinued to sell calculators under the Unicom brand-name, but later abandonedthe Unicom trademark, and began selling their calculators under the Rockwellbrand name. The C112 is atwelve-digit, four function machine, with switch-selectable constant. Itoperates in floating decimal mode. Two neon-tube indicators behind red jewelsat the right end of the display panel indicate overflow and negative signconditions. The keyboard uses magnet-activated reed switches, making forreliable and bounce-free operation. It appears that twodifferent versions of the C112 were manufactured during its market lifetime.The unit exhibited here is one of the earlier machines. Sometime during 1973, adesign change was made to reduce cost, which consolidated all of the logic anddisplay electronics of the calculator onto one plug-in circuit board. Theearlier machines, such as the one exhibited here, utilized one circuit boardfor the main logic of the calculator, and a separate circuit board which containedthe display drive electronics. It appears that the consolidation was madepossible through the use of hybrid circuit modules (black rectangular modulesin the photo below) which miniaturized the display driving electronics suchthat everything could fit on one board. This change surely reduced themanufacturing cost of the machine, allowing it to remain cost- competitive inthe highly volatile calculator market of the 1972 through 1974 timeframe. Bothversions utilized the same Large-Scale Integration (LSI) two-chip calculatorchipset made by AMI. It appears that the C112 remained on the market wellthrough 1974, as models have been found with date coded components datedthrough the latter half of 1974. Since the C112exhibited here is one of the early machines, the brains of are contained on twocircuit boards which plug into a card cage with backplane connections (partlyhard-wired, partly via a small bridge-type printed circuit board). Aninteresting note about the machine is that it appears to have been designed forserviceability. The case is made up of three parts. The first is a panel at therear of the machine which can be removed after taking out two screws to gainaccess to the card cage without having to take the rest of the case apart. Thesecond, with removal of four screws, allows the hood over the display assemblyto be removed for easy access to the display subsystem, and last, the main partof the case making up the 'bottom' of the machine can also be removed. The C112 is an LSIintegrated circuit-based calculator. One board containing most of the logic hasthe AMI-made chip set (AMI Part numbers 0566 and 0567) that run the show. A fewsmaller small-scale IC's on this board provide support functions. The othercircuit board, containing a couple more small-scale IC's and a lot of discretecomponents, provides drive functions for the display. The machine is powered bya linear, transistor-regulated power supply which is located across the back ofthe machine. The C112 is a slightly later version of an earlier Unicom-producedmachine marketed by Commodore, the Commodore 412F. The C112 performsthe standard four functions. A push-on/push-off keyboard switch labeled"CON" enables or disables the constant function, which works formultiplication or division only. The "C" key clears everything, asexpected. Addition and subtraction operate 'adding machine' style, withmultiplication and division using the "+=" key to calculate theresult. A small slider located to the left and below the display controls fourplastic 'arrows' which the user can position to mark comma locations. The C112does not provide leading/trailing zero suppression.The C112 is a ratherfast calculator, which seems to be a common trait of Commodore machines. Whileit seems to have trouble generating the correct result with 12-nines divided by1 (it gives 0.99999999999), 11-nines divided by one works fine, and generates aresult virtually instantly (less than 1/10th of a second). Division by zerocauses all the decimal points to light up with no error indication, except ifthe dividend was zero, which gives an answer of 0. Pressing digit keys duringthe "all decimal points on" state causes the digits to be enteredinto the display. Pressing a function key at this point seems to carry out thefunction as if the dividend was entered as the first number in whateverfunction was entered. Of course, pressing the "C" key during the"all decimal points on" state clears everything, and the machine isback to normal. Another abnormality observed is that this machine (which mayhave been corrected in the second version of the calculator, but the museum hasnot yet acquired one of these) seems not to properly handle negative overflow.For example, entering twelve 9's, followed by the - key results in999999999999.- in the display. Then, pressing 10, followed by the - key,results in a display if 000000000009.- . In this case, it appears that theoverflow detection circuitry doesn't kick in, and the result simply "rollsover". This is a rather serious bug, as this could cause incorrect resultin certain types of calculations. Performing 999999 X999999 gives the correct answer instantly, but incorrectly causes an overflowindication. In playing around with the machine, it seems that it has a tendencyto give overflow indications when the result of a calculation should be withinthe range of the machine. I believe that this has something to do with the factthat the machine appears to have some difficulty with its implementation offloating decimal. If a calculation results in a number which has a lot ofdigits behind the decimal point, IE: .12345678987, and you multiply this by anumber with a few digits in front of the decimal point, for example, 157, theanswer comes up as 9.38271601116, which is incorrect, and to add insult toinjury, the overflow indicator is lit. This calculation should be within therange of the machine, but it appears that whatever algorithm is used toposition the decimal point gets confused in such calculations and ends upmispositioning the decimal in the calculation, which causes an overflow. Idon't believe that this is a problem with this particular machine, but a designdefect which exists in all machines which use this particular AMI chipset. Aswith most electronic calculators, an overflow locks up the machine until the"C" key is pressed.