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Wang C-52 Scientific Calculator

Updated 9/6/2012

The Wang C-52, along with other members of Wang's C-series machines, represent the end of the road for Wang Laboratories' electronic calculator products. Wang made numerous attempts to reduce costs in the early '70s, as the beginnings of the calculator market shakeout began to occur. In machines such as the Wang 100, 500 and 600-Series calculators, cost reductions were realized by making use of integrated circuit RAM to replace the expensive magnetic core memory of earlier machines; use of techniques such as bit-serial versus digit parallel architecture to reduce component count; and various schemes to reduce the complexity involved in storing the microcode which directed the operation of the machines. While these efforts did somewhat ease the erosion of market share, it was still very clear that, with ever-increasing competition from companies in the high-end marketplace such as Hewlett Packard, Olivetti and IME, it was going to become increasingly difficult for Wang to compete in an incredibly dynamic marketplace. Along with that, Dr. Wang realized that the future of calculators was in Large Scale Integration devices...integrated circuits where one or two IC's could implement most of the circuitry for a complete electronic calculator. He knew that a tremendous investment would have to be made in order for Wang to have its own integrated circuit design and manufacturing capability, and that the company wasn't in the financial position to do so. Along with that, it would have put Wang into competition in the fiercely competitive LSI marketplace dominated by Texas Instruments, Toshiba, Fairchild, AMI, Motorola, Rockwell, and many other market players. These companies would likely hold the technological keys to the future of the calculator marketplace, and any company in the calculator business that didn't have a well-established LSI manufacturing capability of their own, or a very strong relationship with one of the key players in the LSI design and manufacturing marketplace, would be left behind. With all of these factors in mind, Dr. Wang knew that the amazing success of his company in the calculator business wouldn't last much longer, and, as a result of his foresight, had begun to refocus the company's efforts on the fledgeling technology of word-processing, using many of the concepts developed for Wang's calculators as the core CPU (Central Processing Unit) for a new breed of machine that processed words rather than numbers.

While Dr. Wang had visions of word processing technology bringing his company to new heights of success, capital was needed to develop the word processing technology. With profits from the calculator business falling off, one last attempt was made to milk some remaining revenue from the calculator marketplace. The goal was to build a calculator that re-utilized as much of the architectural concepts of earlier machines, but utilized as much off-the-shelf IC technology, using as many medium-scale devices as possible to reduce component count and complexity. The result was the Wang 400 and C-Series calculators. The 400-series machines were the high-end calculators, very similar in capability to the Wang 600-series machines, offering learn-mode stored program programmability, high-level math functions, peripheral interfacing capabilities, and high-speed operation. The C-series calculators were intended to recapture the some of lower-end of the market, forsaking learn-mode programmability, and providing limited peripheral interface capabilities, while still using higher-levels of integration to reduce cost. The C-series calculators pulled quite a bit of functionality out of a comparatively small number of chips. The C-52 contains only 71 digital integrated circuits! Compare this with the 100's of IC's used in earlier machines, and it's clear that streamlined design and increasing levels of integration made it possible to shrink the parts count, thus cost and physical size, rather dramatically.

Model/Serial Tag, along with UL Certification, and QA Tag (August 31, 1973)

At the time of this writing, there are seven known models of C-Series calculators produced, including the C-50 Basic Scientist, the C-52 Advanced Scientist (exhibited here, big brother to the C-50), the C-62 Statistician, the C-72 Algebraic Scientist, the C-85 General Purpose Calculator, the C-86 Government Bond Trader, and lastly, the C-87 Surveyor. All of these machines share a common architecture, with some differences in keyboard layout and application microcode giving each machine its individual applications personality. The exact date of introduction of the C-Series calculators is unknown at this time, however, the 400-Series machines, which share many common elements with the C-Series, were introduced in late 1972. The C-Series machines likely followed shortly thereafter, sometime in early '73. Based on date codes on parts and assemblies within this machine, it was likely manufactured in mid-1973, and went through final QA before shipment to its buyer or distributor at the end of August, 1973.

The 400-series and C-series calculators share a common modular architecture and mechanical packaging. The calculators in both lines share cabinetry, basic structural design, power supply design, keyboard construction, and display subsystem. The machines have a motherboard (varying in design between 400 and C-Series) across the bottom of the chassis that contains the power supply, power-on startup and clearing logic, main clocking and sequencing circuitry, shared microcode ROM and addressing circuitry, microcode decoding, data routing, and keyboard/display interfacing. On 400-series machines, the motherboard also contains some logic for implementing the learn-mode programming capabilities of these machines. The motherboard for the C-Series calculators (Board #6282) contains eight sockets for the microcode ROMs, of which six are populated in all C-series models encountered to-date. A total of 21 small- and medium-scale devices reside on the motherboard, not counting the 8 sockets for ROM. With the six chip common ROM set, a total of 27 digital IC's are located on the motherboard.

Wang C-52 Motherboard

The common microcode ROMs for the C-Series carry Wang Part Numbers 377-0030 hrough 377-0034, and 377-0153. 377-0153 supercedes 377-0035, which apparently had a bug in it. Given that these ROMs were custom mask-programmed devices (at the time, EPROMs [Electrically Programmable Read-Only Memories] didn't exist with sufficient capacity to store the over 30 kilobits of microcode in a reasonable amount of space), fixing a bug meant that a new IC photomask had to be created to fix the bug, and a batch of new chips created to supercede the buggy chips. Because of this, it was very important that the microcode be very carefully debugged and checked out before it is committed to a large volume of mask-programmed parts. An error would result in a whole batch of expensive parts having to be scrapped. Apparently, this is what happened to ROM 377-0035.

The #6265 RAM/ROM Board

Also included on the motherboard are an edge-connector socket for a RAM/ROM daughter board, and a pair of sockets for the Arithmetic Logic Unit daughter board. Along with the edge-connector sockets are two 16-pin DIP sockets into which DIP headers plug into for connecting the keyboard and display subsystems.

The C-Series machines use mask-programmed 512 x 10 ROMs (Read-Only Memories) supplied by Electronic Arrays, to contain the microcode store. A standard set of six ROMs (a total of 30,720 bits) populated in the motherboard's ROM sockets make up the common operating microcode (which provides the basic functions of the C-Series calculators, including display generation, keyboard handling, register management, and the four basic math functions) of the machines.

Additional ROM located on a plug-in RAM/ROM board (Board #6265) provide built-in programs to implement the specific higher-level math functions provided by each model of calculator. For example, the C-52 Avanced Scientific exhibited here has two ROM's (Wang Part Numbers 377-0037 and 377-0038) containing the programming for scientific math functions, while the C-86 Government Bond Trader has a four-ROM set (Part Numbers 377-0152 through 377-0154) which contains programming for this machine's complex government bond trading functions. The RAM/ROM board contains five small- and medium-scale IC's for address decoding and buffering.

The main memory of the calculator, also inlcuded on the plug-in RAM/ROM board, utilizes Intel 1101 256x1 RAM (Random Access Memory) devices. Memory is addressed 4 bits at a time. Eight sockets for RAM chips are located on this board, with either four (256x4) or eight (512x4) memory chips populated, depending on the memory needs of the particular applications supported by the calculator.

The #6282 Arithmetic Logic Unit Board

A common plug-in ALU (Arithmetic Logic Unit) daughter board (Board #6282) uses 25 small-and medium-scale integration devices, including a Texas Instruments 74181 TTL 4-bit full-adder. This board provides the basic arithmetic and logical function for the machine. Basic math (add/subtract) and logical operations operations are carried out four bits (one Binary-Coded Decimal digit) at a time.

The #6027 Burroughs Panaplex Display Subsystem

For the display, the C-Series machines share a common display subsystem (Board #6027) utilizing an IC-based 7-segment decoder, with transistorized drivers for the multiplexed 16-digit position Burroughs Panaplex display. This is the same Burroughs-made display panel used as the display in the Wang 600-series calculaors. The display sub-system connects to the motherboard using a sixteen-pin DIP header at the end of a length of spectra cable. The display system suppresses the display of insignificant leading zeroes (but doesn't suppress trailing zeroes) in results, and automatically positions the decimal point. The display rendition is seven-segment, with addition of two vertical bars in the middle of the "8" which allow the digit "1" to be centered within the digit. Decimal points are positioned at the lower right of each digit. The decimal point is displayed alone in a digit position, which is a characteristic that the machine shares with the Wang 600.

The Display Circuitry

The C-Series machines provide display of 13 significant digits, as well as providing scientific notation, with the mantissa containing ten significant digits, and the exponent ranging from -99 to +99. If the number to be displayed is too large to display with thirteen significant digits, the display automatically shifts into scientific format.

The back side of the #6246 Keyboard Assembly

The C-Series calculators were introduced using Wang's triend-and-true microswitch keyboard design, where the keycap was connected to a stalk that had a disc which was pressed onto the stalk, that pressed down on the actuator button of a microswitch when the key was depressed. You can see detail of this type of keyboard construction in the exhibit on the Wang 360SE. This keyboard design (Board #6246) was later replaced (likely due to cost-cutting measures), by a new design (Board #6339), which utilized enclosed leaf-switch modules manufactured by famous switch manufacturer, Oak. These switches, while using high-quality gold-plated leaf contacts, were never as realiable as the old microswitch design. The newer design keyboards are more susceptible to contamination getting inside the keyswitch modules, which can cause unreliable keyboard operation, including missed key depressions, or keyboard "bounce", where a single keypress results in multiple instances of the digit being entered. The later keyboards with the Oak keyswitch modules had a more conventional keyboard feel, with a longer throw on the switches compared to the short throw of the microswitch-based keyboards. The C-52 exhibited here utilizes the "early" (#6246) microswitch-based keyboard assembly. The keyboards are encoded utilizing diodes to encode each keyswitch into a unique 8-bit code. A few transistors, combined with a couple of IC-based one-shot multivibrators conditions the keyboard output (eliminating contact bounce), and standardizing the width of the "Key Pressed" pulse.

The front-side of the C-52 keyboard Assembly

The C-Series calculators provide two independent arithmetic function units, the "LEFT" and "RIGHT" units, which operate identically to their counterparts on the Wang 600, and have their genesis in the 300-series machines. Each arithmetic unit provides [STORE], [RECALL], [+], [-], [X=], [=]. and [TOTAL] functions. The [STORE] function stores the number in the display into the arithmetic register. The [RECALL] key displays the content of the arithmetic register on the display. The [+] key adds the number in the display to the arithmetic register, placing the result in the arithmetic register, then automatically recalls the arithmetic register to the display. The [-] key subtracts the number in the display from the arithmetic register, putting the result into the arithmetic register, and then recalls the result into the display. The [X=] key multiplies the number in the display by the number in the arithmetic register, and places the result in the arithmetic register, and then displays the content of the arithmetic register. The [÷=] key divides the content of the arithmetic register by the number in the display, placing the quotient in the arithmetic register, then automatically displaying the content of the arithmetic register. The [TOTAL] key recalls the content of the arithmetic register to the display, then clears the arithmetic register to zero. With two complete arithmetic units, the machines are very useful for business as well as more complex math operations. Though not confirmed as yet, it appears that the 400 and C-Series calculators gave up on Dr. Wang's famous idea of using logarithms for multiplication and division, instead using conventional shift and add (or subtract, for division) algorithms.

A number of other keys make up the main part of the keyboard. The numeric keypad is of standard layout, with double-sized zero and decimal point keys. Digit entry on the machine proceeds left to right, and entering a decimal point consumes an entire digit position. Entering more than 13 significant digits will result in an overflow error condition. The [CHANGE SIGN] key toggles the sign of the number in the display. When entering exponents in scientific notation, this key will toggle the sign of the exponent portion of the number. The [CLEAR DISPLAY] key does exactly what it says, clearing the display, so only a "+" sign appears at the left end of the display, readying the machine for numeric entry. This key is generally used for clearing numeric entry errors. Lastly, the [SET EXP] key switches the display to scientific notation, and sets up the machine for entry of an exponent. The exponent can range from -99 to +99. If extra digits are entered beyond the two digit limit of the exponent, no error is presented, and the the new entry shifts the other digits to the left. For example, pressing 0.234 [SET EXP] 33426 will result in "+0.234 +26" in the display. Once this number is entered into the calculator by pressing a math function key (e.g., the [LEFT+] key), the number is normalized and displayed as "+2.340000000 +25"

The [PRIME] key resets the machine. It resets the error condition, and clears the display to "+0.000000000000", as well as clearing the machine's sequence control logic. The left and right accumulators are left intact, as are the sixteen storage registers. The [GO] key is used to continue functions which require multiple input (no such functions exist on the C-52) or to provide a means to continue the calculation when an operation has multiple outputs to display. For example, the [n, ΣX, ΣX2] function key first displays the item count (n) when pressed, then pauses so the user can view the result. Pressing the [GO] key will then cause the sum of the entered list of numbers to be displayed, and pressing [GO] again will cause the sum of the squares of the list of numbers to be displayed.

The Function Keys with their Labels

The C-series machines all provide a group of sixteen keys, arranged in two rows of eight above the usual operational keys, which provide access to the specific high-level math functions of the model of machine. Two locking pushbuttons (with only one allowed to be depressed at any time) mode switches, one with a black button top, and the other a white button top, provide a way to select one of two different functions for each of the sixteen function keys, meaning that the machines can support a maximum of 32 individual special functions. Strips of plastic-laminated paper are fitted above each group of eight function keys, retained by plastic pins, served to identify the functions of each key. This meant that no specialized screen-printed keyboard bezels for each model would have to be created -- yet another cost-saving measure.

On the C-52, the function keys provide access to a comprehensive selection of higher-level math functions, including factorial; 10x; ex; trig functions; inverse trig functions; hyperbolic trig functions; inverse hyperbolic trig; square root; base 10 and base e logarithms; polar to rectangular conversion; degree to radian conversion; reciprocal; and mean (average), median and standard deviation; and item count, summation, and sum of squares. The function shown on the white part of the key label is executed if the white function pushbutton is depressed, and the likewise, the function in the black part of the key label is executed when the black function pushbutton is depressed.

To the left of the sixteen function keys are two keys labeled [STORE] and [RECALL]. These keys are used to access a bank of sixteen storage registers. Pressing and holding the [STORE] key, while pressing one of the sixteen special function keys (numbered 0 through 7, left to right, on the bottom row, and 8 through 15 on the top row) will copy the number in the display into the specified storage register. The same operation applies to the [RECALL] key, which will recall the number in the specified storage register to the display.

The C-series calculators provide a connector on the rear panel for addition of a limited set of peripherals. At this time, the only known peripheral for the C-Series calculator is the Model 10 Mark-Sense Card Reader. This device allows input to the calculator to be read from standard pre-printed "IBM card"-sized cards marked with a #2 Pencil. Up to 40 keypresses can be encoded on a single mark-sense card, allowing simple linear step-by-step "programs" to be created. The codes marked on the card are optically read by the reader as it is pulled through by motorized wheels, and executed on the calculator as if each key was pressed on the calculator keyboard.

The machine is very good about catching error conditions. Numeric overflow is always detected, and indicated by flashing the display at a 2Hz rate. Overflow does not lock out the keyboard. Operations may continue as normal, but with the display flashing to indicate that the resultant display is not to be considered accurate. Illegal input to math functions, such as dividing by zero, extracting the square root of a negative number, performing a logarithm of zero, etc., will all trigger the flashing display indication. The error condition can be cleared by pressing the "PRIME" key.

The C-52 is a fast machine. With a base clock frequency of 4MHz, and all solid-state logic the machine chews through math quite quickly. The basic math functions complete virtually instantaneously. Computing 69 Factorial (1 X 2 X 3 X 4 ... X 69), the largest factorial the machine is capable of representing without overflowing, takes a scant 1/3rd of a second. None of the functions of the C-52 take more than 1/2 second to complete.

The Lowell Tech Property Tag

This machine was originally purchased by Lowell Tech, in Lowell Massachusetts, and used for a long period of time until it was retired. Mr. Meskill rescued the machine on the grounds that it was not to be sold for profit. He then contacted the Old Calculator Museum with the intent of donating the machine to the museum. The museum reimbursed Mr. Meskill for the packing & shipping costs, and is grateful for the donation of this interesting calculator.


This exhibit was made possible by the generous donation of the Wang C-52 calculator and Model 10 mark-sense card reader to the Old Calculator Museum by Mr. Sean Meskill.



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