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Calculators: Desktop: Texas Instruments TI-5100

(c) Emil Dudek 2011

Size (approx):

194mm x 196mm x 62mm(max) (w,h,d)
Weight 560g, (848g including cable and UK three-pin plug)


Mains (220/240V  50Hz, 3 Watts) power through two pin, in-line transformer adaptor (AC9900G (UK) supplying 12V 50Hz, 250mA) with a cable of considerable length.  This enters the calculator on the top edge, towards the far right.
Display: 10 digit blue VFD display with an additional symbol cluster for memory, negative and error indication.  Commas are generated by a decimal point and tick. 
Features: Standard four functions with switched constant, percentages, number count, and four function memory. Switched floating and two-decimal mode. Semi-RPN logic.
Age: 1976
Manufacturer: Texas Instruments, assembled in Holland (some were in the USA and Italy).  Serial number 9118496. (One Italian example is 14440 and is rated at 200mA)


Wide format, sharp-edge design with subtle brown and beige colours that looks like it would fit in well with a leather chair in a director's office from the 1970s.

Case and Design: Made from two sections of lightly textured cream plastic in an shallow wedge shape with sharp angles.  A titled and slightly inset neutral plastic display filter gives a good bright display.  It has an embossed silver printed brand logo to the bottom left.  The keyboard surround has a textured brown finish to mimic soft leather and has gold outer key-line and white text for the switch labels.

(c) Emil Dudek 2011

Keys and Switches: Big chunky keys with long travel and a hollow loud clunk and bounce. A subdued colour scheme of cream, grey and pale orange is complemented by the brown slide switches. 
Construction: From underneath, remove the four screws, the back section will then lift off, hinging around the top edge to feed out the power socket pins. 
Boards: The main board (1020961A  ASSY 1020962) sits face down in the upper case section sitting on two plastic posts and held by two screws.  You can lift out the whole assembly by removing these two screws and the caps on the three switches. The keyboard assembly (4276ACH)  is held also by these two screws and an additional two plastic posts.

(c) Emil Dudek 2011, shows tick and point display for decimal point and thousands indicator

Components: 1 x cpu, Texas Instruments TMS1073
1 x 10 digit plus symbol cluster VFD, flat glass face
Numerous transistors, diodes, capacitors and resistors.

Logic comments: (C/CE) is used to clear the calculator or to cancel the entry of the second number inputted into a calculation.
The logic is semi Reverse Polish Notation (RPN): to do 5-8 key in (5)(+=)(8)(-=) to give "-3"
There is switched constant using the (K/C) switch on multiply and divide only
Negative numbers are shown with a minus sign in the far left symbol cluster thereby allowing full ten digit negative numbers
Input overflow is suppressed, inputting an eleventh digit is ignored
There is switch to choose between fully floating decimal and fixed two digit decimal mode, which rounds up 5/4.
Memory store if by use of the (M+=) and (M-=) keys, when indication with the far left symbol cluster "M" reminds you
The "N" key gives you the result of a serial addition/subtraction number count
Overflow shows zero and "<-" in the fare left symbol and is not recoverable
Divide by zero shows zero and "<-" in the fare left symbol and is not recoverable
Overflow in memory shows the last number added and "<-" in the far left symbol and is not recoverable - you lose the memory contents
No bugs found