Early Electronic Calculator TEAL Royal Digital I Calculator

Manufacturer:  TEAL Model:  Royal Digital I OEM:  TEAL Year:  1971 Form:  Desktop Functions:  Basic four Number of Digits:  10 Display Type:  VFI Display: FUTABA DG12C Logic Technology:  DIS,SSI,MSI Memory Technology:  MSI-MOS Diodes:  ~ 300 Transistors:  6 Principal ICs:  JMOS (µPD100,..) IC Complement: NEC µPD10C (3), NEC µPD11A (1), NEC µPD13C (9), NEC µPD101C (2), NEC µPD102C (1), NEC µPD107C (1), Mitsubishi M5811 (2), Mitsubishi M5812 (3), Mitsubishi M58214 (1), Mitsubishi M58221 (1), Rohm TK2415 (1), Rohm TK2813 (4) (29 total) Tech. Data Level:  3 Tech. Data Source:  RE Tech. Data Pages:  16+17 Tech. Data: Schematic (pdf), Theory of Operation (pdf)

At a glance, based on it's size and vacuum-flourescent display tubes, this would appear to be an early LSI-based desktop from the early 1970s. The period would be correct - a 1971 date code was found inside. It's quite a bit smaller than the discrete and SSI-based calculators of the late-60s, so an LSI-based implementation would be expected, as by 1971 the transition to LSI was underway and a few LSI chipsets for calculators were available.

Opening it up led to a surprise though. It's built from the JMOS series of SSI/MSI ICs, along with lots of discrete components. Rather than being amongst the first of a class, this is one of the last, likely the last basic 4-operation calculator model based on this low level of integration. The designers managed to get the IC count down to just 29.

That's not a bad display tube in the right-most digit, it's an intentional half-height zero, produced by some special logic around the outputs of the 7-segment decoder.

Royal is actually Royal Typewriter Company, a then long-established typewriter manufacturer. This calculator model is fairly obviously of Japanese manufacture however. The calcuseum site shows the apparently same model badged as the Litton Feiler RC120, and indicating it was OEM'd by TEAL (Tokyo Electronic Application Laboratory).

Internal view.

Main logic board with registers and state machine.

Timing and display board.