Texas Instruments TI-620

Date of introduction:  1974 Display technology:  n.a.
New price:  $ 299.95 Display size:  
Size:  14.0" x 10.0" x 3.7" Printer technology:  Drum impact red/black
Weight:  6 pounds 8 ounces Serial No:  620-067224L
Batteries:    Date of manufacture:  wk 10 year 1975
AC-Adapter:  120V AC Origin of manufacture:  USA
Precision:  12 Integrated circuits:  TMS0203, TMS0221, TMC0306, TMC0406
Memories:  1 + 1    
Program steps:   Courtesy of:  Larry Corrado

This rare TI-620 was introduced in the year 1974 and seems to be a sibling of the TI-450 and TI-500.

TI-620_2.jpg (43907 Byte)At first glance the TI-620 looks like a modern printing desktop calculator - but it misses the display. On top of the huge keyboard there are only four Status Indicator LED's:

PW: Power On
M:  Memory
OF: OverFlow
K:  Constant

TI-620_1.jpg (77395 Byte)Dismantling this TI-620 manufactured in March 1975 (Thanks, Larry!) is not an easy task but from great interest. The whole calculator is centered around the huge, self-contained printing assembly. It was manufactured by Japanese Suwa Seikosha Co, LTD., better known under the EPSON brand. It has a red/black ribbon and dimensions are 4.3" x 2.8" x 5.2". There are 15 print columns occupied, but it appears that only 13 of those are for digits and separators; the right two columns are for op codes.

TI-620_PCB.jpg (147415 Byte)The TI-620 uses a calculator architecture based on the TMS0200 Chipset for 12-digit desktop calculators but misses the usual 12-digit display. Related calculators using this chip set are the SR-20 and SR-22. The first usage of the chip set were the TI-4000 and the Canon 121F

TI-620_IC.jpg (138198 Byte)The TI-620 is as of today the only calculator known using all four members of the First Generation TMS0200 Building Blocks:

TMS0200 Data Chip Register Processor with four 16-digit Registers and seven Keyboard Scan inputs
TMS0300 ROM Chip 512*13 Bits Instruction Memory with serial interface to Data Chip and 13-digit display and keyboard scanning, up to 4 ROM Chips
TMC0400 ROM/Register Chip - 512*13 Bits Instruction Memory with parallel interface to ROM Chip and two 16-digit Registers
TMS0220 Printer Chip Interface to two-color Drum Printer Mechanism

If you search in Texas Instruments' own "History Section" for their first printing calculator, you'll find the TI-5050 introduced one year after this TI-620. The TI-5040 featured the first combination of a display and a printer in a desktop housing.

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If you have additions to the above article please email:

Joerg Woerner, March  26, 2002. No reprints without written permission.