Commodore SR-1800

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Calculators: Handheld: Commodore SR-1800

		Size (approx):	76mm (max) x 160mm x 38mm (max) (w,h,d) Weight 174g excluding batteries.
		Power:	4.5V DC, 3 x AA size batteries that fit in a compartment cover/cartridge. Also accepts adapter/charger (No. DC-640 or 707, 708 or 709) through a socket on the top side to the far right. Remove disposable batteries before plugging in an adapter.
		Case:	Wedge shaped two-piece matt black plastic case. The top area is dominated by an oversized, wrap over top and side green plastic display filter that gives a large bright image. In this is a black printed metallic sticker that sits in its own recess and contains the brand and model number. The keys are typical Commodore, small and squishy but work very well. Extra labels for the keys are raised and painted green. The lower front edge has another black printed metallic sticker that sits in its own recess with “Commodore” on it.
		Display:	12 digit green VFD with the third and twelfth digit for negative signs. The twelfth is also used for error indication and the first decimal point for radian indication.
		Features:	Standard four functions, parentheses, register exchange, reciprocal, squares, square roots, change sign, pi, trig, logs, powers, nth root, polar/Cartesian coordinates, degree/radian conversion, stats and three function first memory with two function second memory.
		Age:	1976
		Manufacturer:	Commodore made in Japan, serial number 92169.
		Comments:	Late edition Commodore that keeps many of the design principles of the early scientific series but modernises it a lot with clean angles and prominent tilt. It sits equally at home in your hand or on a desktop. The logic is quite sound with some useful functions but no constant and poor recovery. The original cover is soft black plastic with a top flap and front popper closing. It has Made in Japan embossed on the front and Commodore on the back (the wrong way!). Interesting insides prove that this is the update of the SR 9120 model.

Components:	1 x cpu Commodore GHU-03A 7614 (week 14 of 1976) , 40 pin DIL 0.6" width 1 x IC COmmodore KGHU-01W 7618 (week 18 of 1976), 16 pin DIL, 0.3" width 1 x 12 digit VFD unit; single tube flat faced 2 x transistors 8 x diodes 5 x capacitors 8 x resistors 1 x transformer
Construction:	Remove the two screws from the rear and gently prize apart the two sections as there are internal lugs also holding the case together. The rear section then lifts off. There is a small piggy-back board that houses the voltage regulator circuitry.
Boards:	The main cpu board (PCB No. 200855 TW-17 Rev B) sits lose above the keyboard assembly (200785 KB-6424-01 SR9120 N) and is joined via a 21-way ribbon cable.

Logic comments:	(C) is used once to cancel the last number entered and a second time to clear the whole calculator.
	There is no constant on any function
	Input overflow is suppressed, inputting a ninth digit is ignored
	Negative numbers are shown with a "-" in the far left (twelfth) digit thereby allowing full eight digit negative numbers
	Divide by zero shows an "E”" in the far left (twelfth) digit and is not recoverable
	Overflow shows only an "E" (negative or positive) in the far left (twelfth) digit and is not recoverable
	The change sign function can be used in mid number entry – but not before
	Negative square roots are not allowed and result in an overflow
	There is no indication of memory – you have to remember it
	To store in memory one use (STO1) and to recall use (RCL1). (∑1) will act as a (M+) key and add your current display to memory one.
	The (>P) and (>R) convert coordinates to polar or rectangular (Cartesian) form whilst you input then using the (X<>Y) key. This key is also used as a register exchange key.
	Higher functions are accessed by a two key sequence using (F) first.
	The (d-r) key converts from degrees to radians and back as well as switching the mode of operation. The decimal point of the far right (first) digit lights to remind you that you are in radian mode.
	Using the nth power key (y^x) shows the intermediary logarithm on the first press; i.e. two cubed is (2)( y^x)(3)(=) where the display shows “0.693471” before the three is entered
	There are 12 digits of precision: if you input “0.9999999” then (√) then subtract “0.9999999” you will get the extra four digits of accuracy: “4.999-08”.
	The (EEV) and (EE^) keys are useful to display the shifted mantissa – great when you want to convert a small number to milli.. this or micro.. that. Be careful through as you can lose the accuracy which is not recoverable.

	The scan on the left shows the main board: typical for the scientific Commodores calculators, it is dominated by the large connecting ribbon cables. Underneath the top ribbon cable is a mini-board that houses the voltage control circuitry and several other components. Notice the high component count and use of high quality metal brackets to hold the main cpu and display board together. This could not have been cheap to make.
		Interestingly, this scan shows that the keyboard assembly has the text SR9120 (N) implying that this is an assembly used for the SR9120 as well.