DATAMATH CALCULATOR MUSEUM

Texas Instruments TI-55

Date of introduction:	1977	Display technology:	LED-stick
New price:		Display size:	8 + 2
Size:	5.8" x 3.2" x 1.4"
Weight:	6.5 ounces	Serial No:	1111794
Batteries:	BP7	Date of manufacture:	wk 46 year 1979
AC-Adapter:	AC9132	Origin of manufacture:	USA
Precision:	11	Integrated circuits:	TMC1503
Memories:	10
Program steps:	32	Courtesy of:	Joerg Woerner

The TI-55 continued the line of scientific calculators with statistical capabilities started with the SR-51 and continued with the SR-51A and SR-51-II. In Europe the same calculator was marketed as TI-51-III, mathematically and historically correct.

The TI-55 was introduced shortly after [or before - continue here] its sibbling MBA with advanced financial and statistical capabilities.

From a technical aspect the TI-55 continued the ideas of the SR-40 with three main differences: The LED-stick using LED chips mounted and bonded to the printed circuit board, was expanded to 12-digits instead of the 9-digits. The ON/OFF key was replaced by a mechanical slider and the battery connector was changed from a 9V battey style to a small 3-pin header. As a consequence the usage of cheap 9V batteries wasn't possible.

If we discover the sources of the components used in this TI-55 we locate:

	The LED chips were furnished by the SC Group in Dallas.
	The lens by an Ohio supplier.
	The circuit board and the IC are from TI Singapore.
	The board assembly was by TI Taiwan.
	The keyboard was made at TI Lubbock
	and assembled to the board in the Lubbock or Abilene plant.

The TI-55 added 4 keys to do some kind of programming. A small memory hold up to 32 key-codes to repeat simple calculations with different entry values. In comparision to the TI-57 the capabilities were lousy.

If you are interested in the calculating accuracy of scientific calculators don't miss the Calculator forensics.

Simply by comparing the designation of the integrated circuits of the advanced line "Majestic" calculators, you'll get the all members of this family:

	TMC1501 TI-57
	TMC1502 MBA
	TMC1503 TI-55

From the TI-55 two different versions were reported, one with and without chrome-border around the display. Compare with the chromeless TI-55.

Don't miss the later TI-55 II sporting a stylish slanted housing and the modern LC-display.

Introduction of the TI-55

Recently we received from a fellow engineer of a Dallas based company a parcel with some calculator prototypes. One of the surprises was a very early TI-55. The internal construction of the calculator was already final, the only missing item was the date code on the calculator chip. The housing itself carried with the magic LTA2577 number some confusing information. We assume that the TI-55 was introduced after the MBA released in August, 1977. Two explanations:

	The TI-55 was released together with the TI-57 in May or latest June, 1977.
	The TI-55 prototype uses a housing of the TI-57 and carries a wrong date code.

If you have additions to the above article please email: joerg@datamath.org.