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Facit 1121 Electronic Desktop Calculator
Updated 1/2/2022
This rather uncommon machine may bear a bit of familiarity for those who frequent the Old Calculator Museum. For those who might not catch the resemblance, the Facit 1121 looks very similar to the Sharp Compet 20, a calculator that has been a part of the museum's collection for quite a long time.The Facit 1121 was not really made by Facit, but instead marketed by Facit under license from Hayakawa Electric (Sharp). The 1121 was designed and manufactured by Hayakawa Electric in Japan, and badged with the Facit nameplate and model/serial number tag for sale under the Facit brand. The only obvious in appearance between the Sharp Compet 20 and the Facit 1121 is a slight difference in the keyboard layout, along with key cap and cabinet coloring differences. Upon closer inspection, it becomes apparent that the Facit machine has two additional digits of display.
Japanese Advertisement for the Facit 1121
Soon after introduction of its first electronic calculator in
June of 1964, (the Compet 10)
Hayakawa Electric (which changed its name to Sharp Corporation in 1970 after
many decades of use of the brand-name "Sharp") began searching for
ways to broaden the market presence for its calculator outside of
Japan. While there were some reliability issues with the Compet 10
that made world-wide sales of the machine difficult, Hayakawa Electric
had developed a new calculator design based on new Japanese-made Silicon
transistors that were much more stable than the Germanium-based transistors
used in the Compet 10.
The new design was introduced as the Sharp Compet 20 in September
of 1965, and once it hit the market, it was a resounding success, which
further drove Hayakawa Electric to establish a marketing, sales, and service
presence outside of of its homeland. During the course of 1965,
limited experimental export agreements were made with distributors in
Australia, England and Italy for sales of the Compet 20
under the Sharp brand-name. As it became apparent that these trial
exports were successful, negotiations with Facit,
a well-known and respected Swedish manufacturer of fine mechanical and
electromechanical calculators, concluded in a contract for Hayakawa Electric
to manufacture electronic calculators for Facit to sell and service
in Facit's markets. A variant of the Compet 20 was developed that became
the Facit 1121. An initial order of 1,500 1121's was inked, and production
began in late 1965, with sales of the Facit 1121 beginning in the 1st
quarter of 1966. Facit had a strong marketing, sales, and service network
across the globe, indirectly giving Hayakawa Electric access to a much
larger potential market for its new calculator. Since Facit already had a
presence for its mechanical machines in Japan, the 1121 was also marketed
and sold in Japan, literally competing with Hayakawa Electric in its
home market. The benefits gained for distribution of its machines through
the Facit connection more than outweighed the small amount of homeland
competition that Facit's presence in Japan created.
In the mid-1966 time-frame, Hayakawa Electric broadened their
own exports of Sharp-branded machines into France, The Netherlands,
Belgium, and West Germany. Also during 1966, Hayakawa Electric began creating
its own sales and service presence in North America, giving the Sharp
brand name world-wide market presence. Facit already had some distributors
in North America for its mechanical calculators, and the new Facit 1121
ended up being sold in North America. In fact, the Facit 1121 was
available for sale in the North American market before the Sharp Compet 20.
Card-cage of the Facit 1121
Despite the visual similarity between
the Compet 20 and the 1121, there are definitely differences, albeit subtle.
The Compet 20
has a display of 14 digits (plus sign), while the Facit 1121 displays 16 digits
(plus sign). Also, the Facit 1121 lacks the [000] key of the
Compet 20. Other than these differences, the machines operate
identically.
The "A.P." and "Program" Boards
The logic design is Diode-Transistor logic, with pluggable circuit boards
that use discrete Silicon transistor technology along with huge number of
discrete diodes, resistors, and capacitors. The Facit 1121 has one additional
backplane slot versus the Compet 20, for a total of 21 total circuit boards,
with 16 digit boards, one board for the sign digit, a keyboard interface
board, and another board that provides for overflow detection and other
miscellaneous logic. Lastly, two larger boards sandwiched together are
located across the back of the machine. These two boards contain the
sequencing and control logic of the calculator. The Sharp-designed machines
of this generation utilize a hard coded microcode design that reduces the
operation of the machine to a variable
sequence of micro-operations that execute almost like a computer program,
stepping the machine through low-level operations that combine to provide
the means by which the calculator performs its functions. The sequence control
boards in the Facit 1121 are virtually identical to those in the Compet 20, with
the only differences appearing to be a number of jumpers that are strapped
differently between the two board sets. It appears that the control boards
were designed to be a general purpose control system for a series of similar
calculators, with minor wiring changes between them allowing for the
different features (for example, number of digits of capacity). Both
Sharp and Facit had a
number of different models
(Sharp Compet 21 & Compet 30;
Facit 1122) of this general design, so it would
make sense for the design to be adaptable to different functionality with
minimal circuit changes. Each digit board has a 4-bit register composed
of flip flops (arranged as a shift register) that holds one
digit of the X register, which is the entry and display register. Along
with the digit storage, there is logic forming a BCD (Binary-
Coded Decimal) to 1-of-10 decoder, along with driver transistors
to drive the Nixie tube attached to the digit board. The remainder of the
logic on the digit boards contains additional circuitry, such as other working
registers, machine state flip flops, data gating circuitry, decimal point
management and other glue functions.
The size and general design of all of the circuit boards in the Facit 1121
are identical to those in the Compet 20. The circuit boards in the 1121 also
carry the "HEC" designation (Hayakawa Electric Corporation) etched into the
circuit board, same as the boards in the Compet 20. In fact, some of
the boards in the Facit 1121 are exactly the same as the boards in the Compet
20, and are interchangeable between the two machines with no issues.
The ID Tag on the one of the museum's Facit 1121 calculators
Mechanically the Facit 1121 is very similar to the Compet 20. Even
though the 1121 has an additional two digits of capacity, the interior and
exterior dimensions of the two machines are the same, indicating that the
Compet 20 mechanical design was engineered to handle enough circuit boards
to provide up to sixteen digits of capacity.
The base is made from a thick-walled metal casting, as is the
keyboard bezel. The top
cabinet is made from a sturdy thick-walled (likely injection molded) plastic.
The backplane, with the exception of
the additional edge connector, is mechanically
identical, even so far as the power supply bus wiring, and point-to-point
backplane wiring style.
The power supply is physically very similar, although electronically it
seems that some modifications have been made to the Facit 1121 power supply
to allow it to provide more current than the supply in the Compet 20.
The card cage and Nixie tube retaining systems are identical, as well as
the keyboard bezel, cabinet base, and upper cabinet. Most of the mechanical
parts can be interchanged between the machines with no problem.
Keyboard Detail on Facit 1121.
From the operator's viewpoint, the 1121 and the Compet 20 operate
the same. The white [+] key is indexed after a number
is entered to add the entered number to the existing number in the
accumulator and displays the result. The red [-] key subtracts the entered
number from the accumulator and displays the result. Multiplication is
performed by the operator entering the multiplicand, pressing the [X] key
(which lights a red indicator embedded in the key to indicate that
a multiplication operation is pending), entering the multiplier, and
pressing the [=] key to calculate the result. The indicator in the [X]
key remains lighted indicating that the multiplier is still stored
in the calculator as a constant which can be re-used by indexing
another multiplicand and pressing [=].
The [X-] key operates the same as the [X] key, but it
negates the multiplier before performing the multiplication.
Division is performed by entering the dividend, pressing the
[:] key (the ":" symbol is used on Europe in place of the "÷" symbol,
despite this machine having been sold in the US market)
resulting in the indicator in the [:] key illuminating, and the display
clearing for entry of the divisor. The divisor is entered, and the [=]
key indexed to calculate the result. The [CLE] key
is used as a Clear Entry key; it clears the display to allow a number
to be re-entered from scratch. The backarrow key erases the last digit entered
to fix incorrect entry of a digit already input. The [CL] key
is the master clear for the machine, resetting all of the registers,
releasing the overflow indication, clearing any pending multiplication
and division constant (and turning off the indicator in the [X] or [:]
keys) and sets machine state to idle. There
is a green indicator in the [CL] key that illuminates if an arithmetic overflow
occurs, although when an overflow does occur, the keyboard is not locked out
and calculations may continue, creating a potential for an unobservant
operator to carry on calculations after an overflow has occurred.
The [RC] key swaps the two working registers, X and W, useful for reversing
the order of operands in division problems.
Facit 1121 Backplane Wiring
As with the Compet 20, the [M] key, a
push-on/push-off switch, provides for selection of automatic or manual decimal
point positioning. With the [M] key in the up position, the calculator
automatically determines the location of the decimal point to the best
of its abilities. Locking the [M] key in the down position allows the operator
to manually control the decimal point location by entering
the first number of any problem with the desired number of digits behind
the decimal point. If the user desires four digits behind
the decimal point in the result, the first number in the problem would be
entered with that four digits behind the decimal, for example,
entering "6.0000" would set the decimal location to four digits behind the
decimal point.
The Facit 1121 does not have any rounding capabilities, nor does it
have any leading or trailing zero suppression on the display.
The NEC-manufactured CD-65 (same as used in the Compet 20, and
Sharp Compet 15) Nixie tubes
indicate 0 through 9 and include a right-hand decimal point. The tubes
offer a large 5/8ths-inch tall digit which makes the display very
readable. A special Nixie tube at the left end of the display indicates
a "+" or "-" sign to indicate the numerical sign of the number in the
display. There is a slight bug in the sign logic, in that performing
2 + 3 - 5 (entered as [2] [+] [3] [+] [5] [-]) gives a result of
"-0000000000000000.", which is technically impossible, as there is no
such number as negative zero. The bug isn't fatal, though, as adding
1 to it results in the correct answer of "+0000000000000001.".
Display at Power-Up
When first powered up, the Facit 1121
comes up with garbage in the display, typically all digits lit with
7 and 9 in each tube lit at the same time (see photo). Pressing the [CL]
key resets the machine and posts "+0000000000000000." in the display. It
appears that this 7 and 9 lit at the same time indicates that the number
15 (all bits set to '1') is present in each digit of the display register.
This is an invalid Binary-Coded Decimal number (BCD only represents zero
through nine), which the one-of-ten decoder logic translates into two
outputs (7 and 9) being on at the same time. The flip flops all being
set '1' to when powered is likely of the flip flop design having a slight
power-on bias toward setting to '1' rather than '0'. The 7 and 9 being
lit at the same time is an artifact of the decoding logic (a series of
diode gates that detect each of the valid states of the digit register
from zero through nine) being fed a state that it isn't designed decode. For
a four-bit register holding a Binary-Coded Decimal number, the states 0000
through 1001 are valid states for the digits zero through nine, and the
states 1010(10), 1011(11), 1100(12), 1101(13), 1110(14), and 1111(15)
are invalid states that
the decoding logic is not designed to decode.
Overflow is detected reliably by the machine, and when it occurs, a green
indicator in the [CL] key lights up. Overflow indication occurs both on
entry overflow, as well as overflow created by a math operation that exceeds
the capacity of the machine. The overflow indication can be reset by
pressing the [CL] key. Division by zero causes the machine to hang,
with no activity on the display other than the decimal point disappearing.
The overflow indicator does not light when this operation is attempted.
Trying to enter digits or operations while the machine is in this state cause
no response. The only way to clear this state is to press the [CL] key, or
power-cycle the calculator.
The museum has two Facit 1121's, one that is almost fully operational (it has
some decimal point positioning logic issues), and another that needs some
significant work. Their serial numbers differ by 964, and the dating of the
components in the machines put the earlier machine as being built in late
1966, with the later in the early part of 1967. Despite the short difference
in time of production, there is one difference detectable between the two
machines. The earlier machine powers up immediately upon pressing the power
switch, while the later machine has a time-delay relay that causes a delay
of about 2 seconds after the power switch is pressed before the machine comes
to life with a 'click' from the relay. This change was likely due to some
kind of power supply in-rush current issue, whereby adding the relay allowed
the power supply voltages to fully stabilize before the logic supplies were
connected to the circuitry of the machine through the time delay relay's
contacts.
The 1121 is quite fast performing calculations, although just a tiny bit
slower than the Compet 20 due to the two additional digits of capacity, which
require additional cycles for each arithmetic operation. 99999999 X 99999999
(the most complex multiplication the machine can perform without overflow)
takes about 300 milliseconds. Fifteen 9's divided by 1 takes about 600
milliseconds. As with the Compet 20, the full capacity of the machine
cannot be utilized in the dividend during division operations because the
most significant digit of
the working register is used during division as a counter for keeping
track of how many subtractions of the divisor have been performed.
June, 1966
Thanks to Mr. Takaharu Yoshida for providing this scan.
Note lit indicator in [X] key showing pending multiplication operation.
