Early Electronic Calculator Casio AL-1000 Calculator

Manufacturer:  Casio Model:  AL-1000 Year:  1968 ? Form:  Desktop Functions:  Basic four, square root, 4 memories, 30 step linear program capability Number of Digits:  14 Display Type:  NIX Display: NEC LD866 Logic Technology:  DIS Memory Technology:  CORE Diodes:  1530 Transistors:  421 Tech. Data Level:  3 Tech. Data Source:  RE Tech. Data Pages:  26 Tech. Data: list

The unit shown in the photo is my reconstituted unit. What I received was actually just the card cage and a chopped off keyboard. The case and power supply were missing. A replacement power supply was constructed and some plexiglass and aluminum used to hold it all together. I was not inclined to try to recreate a full case, rather this unit serves as a display of the internals of a discrete-component calculator from the 1960's.

This calculator model appears to be very sophisticated for its age, with it's programmability and 4 memories. However, it suffers from a very poorly designed user interface which severely limits it's capabilities.

Anomalies:

There is no overflow indication. There is no indication of incorrect results of too-large multiplications and divisions. If a large number is added or subtracted with a number containing many fractional digits, the result may be incorrect as the decimal point alignment procedure may shift the large number too far up and the most significant digits lost (overflow). The fractional number is not automatically shifted down to avoid the overflow. The M2 register is used internally by the divide procedure. A number stored in M2 by the user will be lost (corrupted) if a divide is performed. Negative numbers are not handled properly in all cases for multiply and divide. The resultant sign and/or value may be incorrect. To enter a fractional number (0<n<1), "0" must be pressed before pressing the decimal point. Taking the square root of a number <= 0.001 will produce an incorrect result (the resultant decimal point will be incorrect). Data in program storage and the 4 memory registers are retained when the unit is powered off. Operand data are not.

Notes:

See the Casio AL-1000 technical description. See the Casio AL-1000 simulation.

Gotta love NIXIEs ..

Top view showing the boards.

The little blue boxes in a row on the board near the rear are pulse transformers for the core memory address lines. Also observable is the 3D layering of the NIXIE numerals.

The core memory board removed for observation.

Closer view of the little core memory planar array. 4 bit-arrays, each 8 by 14.

The red-black twisted pairs are for the sense wires, the red-white twisted pairs for the inhibit wires, and the singular black leads are for the matrix of address wires. Note how each address wire goes through two bit-planes, then reverses and comes back through the other two bit-planes.

A view of one of the boards to give an idea of the component density.

This is board 4: in essence that's the sequencing logic for the function execution state machine in view. Signal flow is primarily right-to-left on this board:

• Starting on the right are a couple of flip-flops (note transistor and capacitor pairs) for the BET and GAM flags and some miscellaneous logic.
• Moving left, the four columns of blue diodes are AND gates. These gates serve to decide the next state of the state machine.
• A column of load resistors for the AND gates.
• A column of diodes composing OR gates, fed by the AND gates.
• Columns of transistors and resistors making each OR gate into a NOR gate.
• The left-most column of blue diodes is a 1-of-32-to-5-bit-binary encoder to encode the selected state into a binary value.

A closer view of components on board 4.

Also visible is a typical source of problems in calculators of this era: observe the only-partially-filled solder fillets around some of the feed-thru leads where they connect to the top foil. A failure of one of these joints in my unit was one of the problems with it.

The new power supply.

The transformer was scavenged from an HP2912 instrumentation reed-scanner of the same vintage as the AL-1000 (it had a secondary for a NIXIE anode supply). Modern integrated regulators were used rather than bothering to make up regulators from discrete components.