Commodore 9R-25

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Calculators: Handheld: Commodore 9R-25

		Size (approx):	78mm (max) x 140mm x 28mm (max) (w,h,d) Weight 164g including in-built rechargeable batteries, 188g without.
		Power:	4.5V DC internal sealed batteries. The adapter (type No. DC-420B centre positive) is used used to recharge the built in Ni-Cd batteries. The socket is on the right hand side, just above midway.
		Case:	Three piece sturdy case in black and white matt plastic. The top front has an oversized green plastic display filter that is flush with the case an has a sloping inset section. It gives a bright image and it has the Commodore logo raised and painted silver. Bold red, white and blue keys have their own raised surrounds. They keys are wobbly and squishy but work well enough. Below the keyboard is a black printed metallic sticker with the company name, which sits in its own recess.
		Display:	8 digit green VFD with a ninth for negative, memory and error indication
		Features:	Standard four function plus percentages, reciprocal, squares, square root and four function memory
		Age:	1976
		Manufacturer:	Commodore. Made in Japan. Serial No. 91499. Ref No. 201121-02
		Comments:	Bold simple design that was to cover many calculators of the Custom Green Line series. This one does not display the top horizontal segment for the digit six (or bottom for nine) making it look a bit unusual. The logic is good but let down by lack of recovery and the negative zero bug.

Components:	1 x cpu: MOS MPS7545 003 1976 (week 19 of 1976), 22 pin DIL, 0.6" width 1 x 9 digit VFD, single tube round face 2 x transistor 6 x diodes 4 x capacitors 4 x resistors 2 x resistor arrays 1 x transformer 1 x double AA-sized rechargeable battery pack.
Boards:	The main cpu board (Part No. 201101, made in Japan) sits on top of the keyboard assembly (201 098 76 430) and is held in place with the adapter socket. The two are joined by a long 14-way ribbon cable and the latter is fixed to the front with ten screws.
Construction:	Remove the two screws from the back and then it gets very very difficult to open as the internal lugs on the sides are very tight. Damage is sure to result so I recommend you do not try. There is a white side lug about half way between the bottom and the adapter socket. You need to push the white section in whilst prizing with a blunt wooden or plastic stick. A second on the side, and one on the top start you going around. The rear eventually lifts off. It is just as tricky to get back together again.

Logic comments:	(C/CE) is used on the first press to cancel the last number entered and the second to clear the whole calculator
	Input overflow is suppressed, inputting a ninth digit is ignored
	Negative numbers show a "-" sign in the far left (ninth) digit thereby allowing full eight digit negative numbers
	Overflow shows the result and "C" (if positive or negative) in the far left (ninth) digit and is not recoverable.
	Divide by zero shows zero and "C" in the far left (ninth) digit and is not recoverable
	There is automatic constant on all four functions
	Negative square roots are not allowed, the result is shown but as an unrecoverable error
	Memory store is indicated by the far left (ninth) digit's decimal point
	Overflow in memory keeps the original number rather than stores the erroneous result - which it displays
	It has the negative zero bug: key in (1)(-)(2)(=) to give "-1" then (+)(1)(=) will give you "-0"

	The scan to the left shows the man cpu board. The display can be seen well mounted in its two black plastic guides at the top. The second resistor array is hidden by the bent plastic ribbon cable at the bottom.