Texas Instruments SR-20

Date of introduction:  Sept.11, 1973 Display technology:  Panaplex II
New price:  $179.95 Display size:  10+2
Size:  9.1" x 6.5" x 2.6"
 232 x 165 x 67 mm3
Weight:  31.0 ounces, 881 grams Serial No:  200047163
Batteries:   Date of manufacture:  wk 44 year 1973
AC-Adapter:  120 V Origin of manufacture:  USA
Precision:   Integrated circuits:  TMS0202, TMS0304
Program steps:   Courtesy of:  Joerg Woerner
    Download manual:   (US: 5.8M Bytes)

The SR-20 is one of the few scientific desktop calculators manufactured by Texas Instruments. In a housing with the size of a TI-3500 but the extreme wedge shape of the SR-10 you find some useful scientific functions but no memory.

sr-20_pcb.jpg (163432 Byte)The displays used in the SR-20 are Panaplex II devices. Produced by Burroughs they are long-life, cold-cathode, glow-discharge display panels. Keep your fingers away, normal voltage is about 150 Volts. With their orange glow they give a perfect readability even in bright ambient situations.
A similar calculator performing conversions between octal, decimal and hexadecimal number bases was the SR-22

sr-20_IC.jpg (34753 Byte)Due to the limited digit capabilities of the TMS0100 calculator-on-a-chip series, Texas Instruments developed the TMS0200 Chipset for 12-digit desktop calculators. This TI-4000 introduced in 1973 marks the first application based on the TMS0200 Building Blocks and makes use of the TMS0200 Data Chip named TMS0201 and the TMS0300 ROM Chip named TMS0301 accordingly. Later designs added either the TMS0220 Printer Chip (TI-500), or the TMC0400 ROM/Register Chip (SR-22), or both of them (TI-620).

Texas Instruments made the TMS0200 Building Blocks available to third parties, don't miss the Canon L121F.

It took about 10 years before the next (non-programmable) scientific desktop calculator manufactured by TI was introduced. Do you know it? View it here.

Some parts of the calculator housing and the display could be found in an industrial product, view the 5TI PLC programmer.    

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If you have additions to the above article please email:

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