Commodore SR7919

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Calculators: Handheld: Commodore SR7919

	Size (approx):	62mm (max) x 135mm x 23mm (max) (w,h,d) Weight 82g excluding batteries
	Power:	9V DC, 1 x PP3 size battery. Also accepts adapter (DC-640 or 707, 708 or 709) through left side socket midway up. There is a power save function where after about 25 second when the display switches off.
	Case:	Typical two piece beige and black plastic commodore shaped case. Top heavy design to accommodate 9V battery in the top section. Keyboard surround is stippled black plastic. Lovely way of representing double function by metallic blue and red on silver keys. These keys are wobbly and squishy but work well enough. The top logo is raised and (originally) pained silver whilst the brand name below the display is a black printed metallic label that sits in its own recess. The heavily inset, convex red plastic display filter gives a bright image but with a limited angle of view.
	Display:	8 digit red LED with bubble lens with a ninth for negative, function select and error indicators
	Features:	Standard four functions and trigs, squares, square root, reciprocal, logs, powers, pi, register exchange, change sign. 5+2 scientific display mode with full eight digit mantissa. Three function memory.
	Age:	1976
	Manufacturer:	Commodore. Made in the United Kingdom (assembled at best). 400200-01. Serial No. 94990
	Comments:	Standard Commodore case is enhanced by the lovely double function buttons in lovely brushed aluminium and blue or red printed text. Unusual for Commodore who normally put as many keys on a calculator as possible! A function like arc-sin can take about three seconds to complete. No constant and lack of overflow recovery is a set-back but otherwise the logic is very sound.

Components:	1 x cpu: MOS MCS 7529 009 2676 (week 26 of 1976) 28 pin DIL, 06" width white ceramic package 1 x IC: ITT 548-5N 7623 (wee 23 of 1976) 22 pin DIL, 0.3" width 1 x 9 digit LED unit with individual bubble lens 1 x capacitor 1 x resistor
Boards:	The main cpu board (ref Part No. 200826) sits lose on top of the main keyboard assembly and is joined via a 16 way ribbon cable.
Construction:	Remove the single screw from inside the battery compartment. Then use a blunt soft instrument (I use service station coffee stirrers) to pop the two lugs you can see through the holes in the lower rear section of the calculator. Then hinge off the rear section from the top edge.

Logic comments:	The (C/CE) button is used to clear last entry of a number on its first press and clear the whole calculator on the second.
	After about 30 seconds it goes into power down mode - underscore sign in the far left (ninth) digit only which is recovered by any key press
	Overflow on number input is suppressed, typing in a nine digit number ignores the ninth digit
	An overflow error is flagged with "r" in the far left (ninth) digit, "F" if negative, and is not recoverable
	The use of the function key is flagged by the far left (ninth) decimal point lighting up
	There is no indication of memory store - you need to remember it
	There is no constant on any functions
	The (8-5) button is used to see the whole eight most significant places of an exponential number.
	Negative numbers are flagged by a "-" sign in the far left (ninth) digit thereby allowing full eight digit negative numbers
	Overflow in memory retains original number
	Square roots of negative numbers are not allowed, showing the result and error which is not recoverable
	Change sign operator can be used in mid input of number

	This scan shows the small board and minimum number of components, The white IC is the main cpu whilst the black one appears to be a display driver. You can see the sturdy ribbon connector at the bottom that goes to the keyboard assembly.