Early Electronic Calculator Facit 1123 Calculator

Manufacturer:  Facit Model:  1123 OEM:  Sharp Year:  1969 Form:  Desktop Functions:  Basic four, constant Number of Digits:  14 Display Type:  NIX Display: Hitachi CD81 Logic Technology:  SSI Memory Technology:  MSI-BIP Diodes:  36 Transistors:  45 Principal ICs:  M5300 Series IC Complement: Mitsubishi M5304 (2), Mitsubishi M5310 (13), Mitsubishi M5320 (19), Mitsubishi M5330 (17), Mitsubishi M5340 (51), Mitsubishi M5352 (7), Mitsubishi M5373 (13), Mitsubishi M5391 (14), Mitsubishi M5962 (3) (139 total) Tech. Data Level:  2.7 Tech. Data Source:  RE Tech. Data Pages:  15 Tech. Data: Schematic (pdf)

An unusual feature of the model is lamps in the multiply and divide keys which illuminate to indicate the according operation is pending. While a curious feature in itself, it is actually part of the provision of a 'constant' feature. The lamps remain lit after the completion of the operation, and another multiply or divide can be performed with the earlier second operand. Pressing the += key a second time after completion of an operation clears the constant state, indicated by the lamp turning off.

A cute internal technical aspect of this model is a two-speed clock. The master clock is an astable flip-flop, but with - so to speak - two flip sides and one flop side, with different timing components connecting the two flip sides to the flop side. The slower flip side is enabled for idle display, while the faster flip side is enabled during calculation.

Anomalies:

Entering more numerals after pressing the decimal point than the decimal point position switch is set for will produce odd results. Division by 0 will result in an infinite loop. Multiplication or division where the first operand entered was negated will produce odd results. Multiplication or division with an operand greater than 12 digits will produce incorrect results.

Notes:

See the Facit 1123 simulation. Read the tale of fixing the Facit 1123.

Top of case removed.	The electronics package removed from the case. There are 3 plug-in circuit boards in a frame, with the power supply at the rear.	Board 1 / upper. Master clock, digit timing, and Nixie display with drivers. The ICs in the 1123 are from a small/proprietary DTL series. On this board, two ICs have been replaced with 7400 series TTL to effect repairs. The H.E.C. in the foil would be Hayakawa Electric Co. (Sharp).
Board 2 / middle. This is primarily the data-processing logic: main registers, ALU, and the decimal-point register. The M5391 ICs in rows 2 & 8 comprise the two main registers (7 * 8-bit shift registers). The empty IC locations in row 1 are for a third, 'memory' register option, included in a higher-end model.	Board 3 / lower. The control / state machine logic, and keyboard encoder and flags.	The keyboard is also a pluggable module.
Keyboard from below. The keyswitches are of the magnetic-reed switch type.	The power supply seen from the rear of the empty frame. The connector for the CMU (Controller/Monitor Unit) is partially visible behind the mains connector.	A simple Controller/Monitor Unit (CMU) can be plugged into a service connector on the bottom of the calculator. The switch selects normal or manual operation. In manual, the calculator stops after every major state cycle. The state of the machine can then be inspected, via the display and/or scoping. Pressing the CLE key continues processing for another state cycle. For example in multiplication, the sub-operations of addition and shifting can be stepped through one at a time. In the photo, the calculator is part way through the multiplication 567*123. The 7 of the multiplier (567) has been shifted out of the lower end of the display into another 4 bits of register, where it is being decremented while controlling additions of the multiplicand (123). The product is building in the upper digits of the display, here the 6th addition of the multiplicand, out of the 7 for this digit of the multiplier, has just been performed: 6*123 =738.
The Controller/Monitor Unit, along with a similar CMU for the Sharp Compet 17. The terminal pins present some useful test points for scoping. These CMUs were constructed after reverse-engineering the calculators, and then assessing what the otherwise-unknown connector on the machines could be used for. The CMU schematic is included in the EEC schematic for the respective calculator.