Texas Instruments TI-58C (1979)

Date of introduction:  1979 Display technology:  LED-stick
New price:  
 $90 (October 1981)
Display size:  10 (8 + 2)
Size:  6.4" x 3.2" x 1.5"
 162 x 81 x 37 mm3
Weight:  8.5 ounces, 240 grams Serial No:  7183855
Batteries:  BP1A Date of manufacture:  wk 17 year 1979
AC-Adapter:  AC9131 Origin of manufacture:  USA (ATA)
Precision:  13 Integrated circuits:  TMC0501E, TMC0580 (CD2400), TMC0580 (CD2401), TMC0573, TMC0591, RCA 10341XX
Logic:  AOS - 8 Pending Operations, 9 ()    
Memories:  0-60    
Program steps:  480-0 Courtesy of:  Mark Bollman
Download leaflet:   (US: 2.0M Bytes) Download manual:  

The main disadvantage of the TI-58, its non-permanent program storage, was corrected with the TI-58C. Replacing the two TMC0598 Multi-Register Chips of the TI-58 manufactured in a power-hungry PMOS process with a low-power CMOS RAM (Random Access Memory) chip, battery drainage caused by the NiCd batteries itself was quicker than drop caused by powering the RAM.

Dismantling the featured TI Programmable 58C calculator manufactured already in April 1979 by Texas Instruments in Abilene, TX reveals a very early design with a printed circuit board (PCB) manufactured in Canada and sporting some patch wires to fix a design problem, also known as blue wires.

Digging deeper into the circuitry of this early TI-58C tells an interesting story: Instead of porting the TMC0598 Multi-Register Chips designed in power-hungry PMOS technology used with the TI-58 into modern CMOS technology, the engineering team decided to use a standard SRAM (Static Random Access Memory) manufactured in a power-saving CMOS process and developed with the TMC0590 Continuous Memory Interface Chip a TMS0500 Building Block to translate the signals of the TMC0501E Arithmetic Chip to the common signals of SRAMs with a capacity of 1k*4 Bits.

The featured TI-58C manufactured in April 1979 uses the following main Integrated Circuits (ICs):

TMC0501E Enhanced Arithmetic Chip: Register Processor with five 16-digit Registers and segment decoder/driver.

TMC0580 (CD2400/CD2401) Double Scanning and Read Only Memory Chips: 2.5k*13 Bits Instruction Memory with serial interface to Arithmetic Chip, 16 Constants with 16 digits, each and 16-digit display scanning. Two chips stacked in a piggy-back manner on top of each other.

TMC0560 (TMC0573) Bare Read Only Memory Chip: 1k*13 Bits Instruction Memory with serial interface to Arithmetic Chip in a small 8-pin package.

TMC0590 (TMC0591) Continuous Memory Interface Chip: Adopts 1k*4 Bits CMOS SRAM with backup battery to Arithmetic Chip.

RCA 10341xx CMOS RAM: 1k*4 Bits CMOS SRAM with Texas Instruments internal part number, most likely a MW5114 chip.

This first version of the TI Programmable 58C using a CMOS RAM chip manufactured by RCA was soon replaced with the second version of the TI-58C based on a Toshiba or NEC chip.

Read more about your first steps of programming this calculator here

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

Comparing the Constant ROM Content with the programmed constants frequently used with computing algorithm of trigonometric functions like sine, cosine, or tangent of an SR-50 manufactured in May 1974 still using the original TMC0521-2 SCOM Chip with the TMC0580 (CD2400) DSCOM Chip of the featured TI-58C with our TMS0500 Platform after recording their ROM Images showed no differences.

Looking into the Key Codes programmed into the second half of the TMC0580 (CD2400) and the complete TMC0580 (CD2401) and comparing with its TMC0582 and TMC0583 counterparts known from the TI-58 and TI-59 shows unexpected differences that we need to analyze. Comparing the Instruction ROM Content distributed over the two TMC0580 SCOM and one TMC0560 BROM Chips of the featured TI-58C with a TI-59 manufactured in May 1979 showed as expected many differences.

The TI-58C continued the usage of the Solid State Software Modules™ with up to 5000 program steps introduced with the TI-58 and TI-59 already in 1977. On the backside of the TI-58/59 you'll note a small lid with a place for a module. The Master Library with 25 different programs was included, a lot of other modules were available. We know four different approaches of the module expansion:

Standard modules like the Master Library use only the small sticker above
    the A,B,C,D, and E keys.
Other modules like the Pool Water Analysis developed by Olin Corporation
    make use of a colorful keyboard mask.
Customized calculators like the USMC AV-8C calculator or insurance calculators
    sold by Allianz and others use special keyboard arrangements. |
The CAL-Q-TAX and incotax calculators use an extender instead the usual 
    drop-in modules. 

The TI-58C carries the connector to the printing cradle. It seems to work on the  PC-100C revision.

American Micro Products introduced with the Module Selector a very interesting product fitting into the charging bay of the printing cradles.

The calculator was available till 1983 before it was discontinued and replaced with the TI-66 Programmable. Don't miss the rare and innovative Franken-Calculator Data Dimensioner.

Andreas Gerlich scanned recently the German documentation of the TI-59, please visit his website. Thanks!

Fellow calculator collector Marek Czeszek prepared wonderful Step-by Step Instructions how to clean a TI-58C.

The TI-58C is featured in the Texas Instruments Incorporated bulletin CL-414 dated 1978.

Find here an excerpt from the Texas Instruments Incorporated leaflet CL-199J dated 1981:

TI Programmable 58C

Advanced programmable calculator with plug in Solid State Software* and Constant Memory*.

Features TI’s exclusive Solid State Software*, tiny, pre-programmed modules you slide into the calculator to extend power, flexibility, and range. It is also keyboard-programmable. Constant Memory* feature retains data and program information even when off.
There are many computer-like features: 170 functions and operations to program up to 480 steps or 60 memories (increases to 5000 more steps with modules). With 4 types of display testing, 6 levels of subroutines, plus 9 levels of parentheses, it can handle almost any problem.
Personal Programming shows how to get the most from the 58C.

* Registered Trademark of Texas Instruments Incorporated

© Texas Instruments, 1981

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© Joerg Woerner, February 27, 2021. No reprints without written permission.