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Hitachi Chips: HD3686
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| Casio 121-MR |
| Make and number: | Hitachi HD3686 |
| Package: | 42 pin DIL, 0.6” width, black plastic |
| Known date codes: | 5M21 (December 1975) |
| Known date of fabrication: | 1975 |
| Calculators: | Casio 121-MR |
| Secondary ICs: | None |
| Power supply: | 6.0V |
| Display capability: | 12 digit + 1 point LED |
| Basic Functions: | Four standard plus CE, C |
| Constant: | Automatic on all four functions |
| Advanced functions: | Percentages, square root, register exchange, sign change. Switch fixed decimal (float/cut/round), switched number of decimals (0/1/2/3/4/6) |
| Scientific functions: | None |
| Memory: | Switched accumulation or count memory Four function (MC) (MR) (M+) (M-) No indication of memory store |
| Overflow states: |
Input
overflow is suppressed |
| Overflow recovery: | None |
| Negative sign: | Point LED |
| Bugs: | tbd |
| Comments: | Negative square root gives the answer but locks the calculator. Fixed decimal point is inconsistent. |