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Texas Instruments SR-22

Date of introduction:  Sept.11, 1973 Display technology:  Panaplex II
New price:  $350 Display size:  10+2
Size:  9.1" x 6.5" x 2.6"    
Weight:  1 pound 15 ounces Serial No:  5601
Batteries:  BP-200 Date of manufacture:  year 1974
AC-Adapter:  AC9222 Origin of manufacture:  USA
Precision:  13 Integrated circuits:  TMS0207, TMC0323, TMC0404
Memories:      
Program steps:   Courtesy of:  Joerg Woerner
    Download manual:   (US: 1.8 MByte)

Look carefully at the display of the SR-22 and you'll notice immediately that this calculator could perform amazing calculations. It is the only calculator reported so far to perform Octal-Decimal-Hexadecimal conversions on the base of floating point numbers. Later calculators like the TI Programmer work only on integer numbers.

The SR-22 is one of the few scientific desktop calculators manufactured by Texas Instruments. It uses a housing with the size of a TI-3500 but the extreme wedge shape of the SR-10

Dismantling this SR-22 manufactured early in 1975 reveals a very rigid construction based on one rather complex printed circuit board (PCB) with two satellites:

The Panaplex II display manufactured by Burroughs.
The keyboard assembly with the keys, slider switch and discrete LED's.



The Main-PCB itself consists of four major building blocks:

Upper part Discrete high-voltage drivers for the Panaplex II display.
Middle-left Clock circuit
Lower-left Voltage supply
Middle-right Calculating circuit

The calculating circuit is formed by an impressive trio of 40-pin Integrated Circuits based on the TMS0201 chip-set introduced in 1973 for calculators like the TI-4000 and TI-450. Most of the known designs use only two chips, a TMS02xx Data-Processor and a TMS03xx ROM-Chip. Only the SR-22 and the TI-620 are reported so far to sport a second ROM-Chip labelled TMS04xx.

The same housing was used with the simpler SR-20 calculator, while the huge power supply AC9222 was exclusively designed for the SR-22.

Read more about George Boole, the inventor of the Boolean algebra.

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

Joerg Woerner, December 5, 2001. No reprints without written permission.