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Calculators: Handheld: Commodore 784D
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| Size (approx): |
64mm
(max) x 137mm x 23mm (max) (w,h,d) Weight 84g excluding batteries. |
| Power: | 9.0V DC, 1xPP3 size battery. It accepts an adapter (No. 505 or DC-620R) through a socket on the left hand side about mid way up. Remove battery before using an adapter. |
| Case: | Beige and dark brown matt plastic two-piece case with matt black keyboard surround. Typical bright Commodore keys that are wobbly and squishy but positive. A heavily inset sloping red flat plastic display filter gives a good clean display, though with limited angle of view. Silver painted raised logo has not survived well. Just below the display is a black printed metallic label that sits in its own recess. |
| Display: | 8 digit red bubble-lens LED with a ninth digit for error and negative signs. |
| Features: | Standard four functions |
| Age: | 1974-5 |
| Manufacturer: | CBM made in the United Kingdom, serial number 03038 |
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Comments:
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This tall slim shape was used for many early Commodore calculators - primarily to cope with the bulk of the battery at the top. Bold three-colour button system works well. Solid logic for this grade of calculator only let down by the negative zero bug.. Original case is soft black mottled plastic with flip over top cover and popper closing. It has an embossed Commodore logo on the front. This is quite an early model using this familiar style. The red LEDs are slightly better than normal as they are the type where each line is made up of several small dots. |
| Components: | 1 x
cpu: Commodore RBP-01-B 7449
(week 49 of 1974) 24 pin DIL 1 x display driver NS DS8855N 502 22 pin DIL 1 x 9 digit single unit bubble lens LED display NSA198 NS448 1 x capacitor 1 x resistor |
| Boards: | The keyboard board is fixed to the front using three screws and two rivets. This is attached to the main cpu board (PCB 200439, ART200440 NS TW-17 Rev 0) via a 17-way ribbon cable. In order to keep the whole assembly as slim as possible, this board has a cut out to fit one of the electrolytic capacitors. |
| Construction: | From the rear, use a small screwdriver to push the lugs to the outside in the lower lug recesses. The back then lifts off by hinging off the two small top lugs. |
| Logic comments: | (C) is used once to cancel the last number entered and a second time to clear the whole calculator. |
| There is automatic constant on all four functions | |
| Input overflow is suppressed, inputting an ninth digit is ignored | |
| Negative numbers are shown with a "-" in the immediate left hand digit travelling into the far left (ninth) digit to allow eight digit negative numbers. | |
| Divide by zero shows "E00000000" (no decimal point) and is recoverable by dividing by 1 | |
| Overflow shows the result with "E" (negative or positive) in the left most (ninth) digit and is recoverable by continual division by 10. | |
| It suffers the negative zero bug: try (1)(-)(2)(=) to give "-1" now (+)(1)(=) will give "-0" |
