Toshiba BC-1270

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Calculators: Desktop: Toshiba BC-1270 (type IV)

	Size (approx):	230mm x 160mm x 60mm(max) (w,h,d) Weight 830g excluding cable
	Power:	Mains (220V 50-60Hz, 3W) power only through a permanently fixed mains cable of considerable length. The on off switch is on the right hand side at the top.
	Display:	12 digit green VFD with an additional symbol cluster for overflow, negative and memory indication. Upper commas are used for thousand separators.
	Features:	Standard four functions with percentages, square root, register exchange and four function memory. Switched constant, memory summation and rounding. Switched fixed/floating decimal notation. Semi reverse polish notation (arithmetic).
	Age:	1980
	Manufacturer:	Toshiba Corporation, Japan, serial number 527394. Safety messages embossed on the back of the calculator are in French and English.
	Comments:	There appears to be several earlier (1976, 7 and 8) versions of this calculator that use a Texas TMS1273NL IC. The same case was used for a wide range of models from the BC-1204 (around 1973) to this last model which explains why it looks so old for a 1980 calculator. The logic is very good if a bit archaic with it semi-RPN mode. It does have an odd "retained negative zero" bug though. Nice bright display with large digits.

Case and Design:	Main body is made from two-piece gloss finish light grey plastic with a third matt black section for the front. At the top, just below the ventilation slots is a blue and black printed metallic sticker with the brand and model number. It sits inset in its own recess. The practically vertical green plastic display filter is heavily inst and printed with white text for the numerals. There are numeral numbers printed in white on it. The switch labels are on another black printed metallic sticker.
Keys and Switches:	Apart from the main number keys there is not much logic to the grouping and it has a messy colour scheme. Big clunky keys are long travel and very easy to use. It must have looked old even in 1980.
Construction:	Remove the three screws from the underside. Turn the calculator back over and gently lift the top section away, hinging at the bottom.

Boards:	The main CPU board (Kentron 144-12A) sits in the rear section and is held in place by a screw and plastic guides. It houses a sturdy metal display frame to hold the VFD unit almost upright. It joins to the Keyboard assembly (CH14154C) via a 21-way ribbon cable. The sturdy keyboard unit has a strong metal frame and 7 diodes mounted on the back.
Components:	1 x cpu: NEC D1220C K071116, 42 pin DIL, 0.6" width black 1 x 12 digit plus symbol cluster VFD unit: Itron FG137D7 1 x transistor 1 x rectifier 22 x diodes (plus 7 on keyboard) 8 x capacitors 6 x resistors 1 x transformer: CT607 1 x mains transformer: T-76U 01208N1 1 x fuse

Logic comments:	(CE) is used once to cancel the last number entered and (C) to clear the whole calculator.
	Operation is semi-Reverse Polish notation (arithmetic) input. To do 5-3 key in (5)(+=)(3)(-=)
	Input overflow is not suppressed, keying a thirteenth digit results in an overflow which is recoverable using (CE)
	Constant function is switched in with the "K" switch and operates on multiple and divide only. The constant is the first entry on multiply and the second entry for division.
	Negative numbers are shown with a minus in the immediate left hand digit, travelling into the far right (thirteenth) symbol cluster thereby allowing full twelve digit negative numbers
	Divide by zero shows zero and "¬" in the far left symbol cluster and is recoverable using (CE)
	Overflow shows the result shifted and "¬" in the far left symbol cluster and is recoverable using (CE)
	Memory store is indicated by a "M" in the far left symbol cluster
	Use (S) to recall the memory and (T) to recall/clear at the same time
	Memory can be switched to auto-summation mode with the "S" key, when the result of every equals key is added
	Overflow in memory displays the shifted overflow but retains the original result and
	You can switch between round down and round options by using the [5/4] switch
	You can switch between floating [F] or 4,3,2 and zero fixed decimal digit modes and [+] which is financial input: keying in (1)(2)(3) results in "1.23"
	(EX) is a register exchange key
	Negative square roots are not allowed and show the result and "¬" in the far left symbol cluster and is recoverable using (CE)
	It suffers an odd form of negative zero bug: with [K] switched on key in (1)(-=)(/)(1)(0)(+=)(+=)(+=) etc to eventually give "0.". Now if you use square root you will get an error as it thinks you want the square root of "-0." even though it does not display this.