TI-59 History


Texas Instruments, Inc invented the electronic handheld calculator in 1967. Originally conceived as a product that would create worldwide demand for the microchip, the handheld calculators became a powerful tool for engineers and businessmen. A decade later, it was time for something new, so Texas Instruments first produced the SR-52 programmable calculator with magnetic card storage (1975) and finally TI-59, introduced on May 24, 1977. The press release stated: 'In order to encourage interest in programming and computational problem solving, Texas Instruments introduced a number of new general purpose and specialty calculators... Nearly 400,000 people purchased programmable calculators in 1976, and over 3 million people would be buying programmables by 1979'.

The TI-59 was an amazing calculator for that time: fantastic 960 program steps and up to 100 date registers (nearly 1 kilobyte of RAM), a variety of built-in functions (including advanced statistics), solid-state ROM modules, a magnetic card reader and an optional print/security cradle PC100A. An introductory price of $299.95 for the calculator itself (another $199.95 for PC100A) was carefully chosen - it was expensive, but affordable, in contrast to first personal computers (Apple II, TRS-80 etc), costing several thousands dollars. Therefore, many professionals bought the TI-59, determined to understand its symbolic programming language and apply it in their work.


The TI-59 used a custom TMC 0501 4-bit processor, and the internal memory could be allocated either to program steps or to data registers. The unit of allocation was 10 data registers or 80 program steps. The TI-59 had up to 960 program steps or 100 data registers. When all 100 registers were in use, 160 program steps were still available, because TI used only two decimal digits for register addressing. The TI-59 could use the first ten registers for fast looping (later it was discovered that DSZ could be used on all the registers), incrementing and decrementing. Up to ten flags could be set, reset or tested. It also had a subroutine return stack that supported up to six levels of subroutine calls. Program steps could be addressed in absolute, indirect and label modes, while data registers could have been addressed directly or indirectly. About 175 functions and operations were available.

Magnetic cards, first considered to be just a nifty feature, became the main TI-59's advantage. You could feed a little magnetic strip into the unit - you'd slip it in a little slot on the right side under the LED display, and a buzzer would sound as it drew the card in, spitting it out at the left side. Programs were usually stored on magnetic cards, so the user wouldn't have to type them in every time he/she turned the calculator on. Using two cards, up to 960 program steps or 100 data registers could be recorded.

Interchangeable, plug-in Solid State Software modules, with up to 5,000 program steps, made TI-59 a useful tool for many professionals. The Master Library module, included with every TI-59, contained 25 programs: matrix calculations, solutions to linear equations, complex arithmetic, zeros of functions, financial and calendar calculations, random number generator, unit conversions and even a simple game called Hi-Lo. Texas Instruments published other modules, including Applied Statistics, Math/Utilities, Real Estate, Investment, Electrical Engineering, Surveying, Marine Navigation, Aviation, Business Decision, Farming and Leisure Library. Each module contained up to 5K of well-written, highly optimized software and the standard price was $40.

The LED display used traditional 7-segment digits, but the TI-59 was the first pocket calculator that was familiar with the alphabet - it was capable of printing text on the PC-100A printer. This thermal printer had 64 alphabetic, numeric and special characters, which could be printed at the rate of 60 characters per second. Up to 20 characters could be printed per line on 6.4 cm (2.5 inch) wide thermal paper. The printer was also used to list or trace program steps as an aid to debugging. Actually, this unit was more than just a printer: it was a docking station. You'd take the battery pack out of the back of the calculator, leaving a large square cavity. You'd place this cavity over the mounting bracket on the printer, lock it into place using a key (that is why the unit was called print / security cradle), and the calculator would get its electric power from the printer. There was even a charging hookup for the battery pack, so that it could be recharged while the calculator was mounted on the printer. The PC100C was introduced a few years later. It was only internally different from the 100A model.

The TI-59 Users Guide, supplied with the calculator, was adequate for both beginners and seasoned programmers. In-depth articles about the internal functions of the calculator were published by independent user groups and magazines, and on May 8, 1979, US Patent #4,153,937 ('A microprocessor system with higher order capabilities provided with two non-volatile memories which are read-only memories in the disclosed embodiment... for use as an electronic calculator') was granted to Texas Instruments. By studying 45 pages, 27 claims and 20 drawings of patent documentation submitted on April 1, 1977 (what a date to apply for a patent!), users were able to decipher most of TI-59's secrets.

Other Texas Instruments calculators

The TI-59 had two smaller cousins. The TI-58 was introduced on May 24, 1977. It had half the memory (60 data registers or 480 program steps) and no card reader, which meant that programs were lost when the calculator was powered down. The TI-58C was introduced in 1979 - it was a TI-58 with continuous memory and some minor internal software improvements.

The TI-88 was supposed to succeed the TI-59. It was introduced in the summer 1982: alphanumeric display, 416 registers (3 kilobytes) and advanced symbolic language attracted many TI-59 owners, but the calculator was withdrawn from production in September 1982 because of static electricity problems. Many calculators malfunctioned only a few days after putting them in use. The production of TI-59 was terminated a year later, in 1983, and PPX library was discontinued in December 1985.

In mid 1983 TI announced the development of a new low cost programmable calculator. The TI-66 offered a horizontal case configuration, a ten digit LCD display, 512 program steps and a memory which would be retained across shutdown similar to that feature of the TI-58C. A companion battery-operated PC-200 printer was also announced. The TI-66 became available to the public in December 1983, while the PC-200 did not become available until mid 1985. Users soon discovered that the execution speed of the TI-66 was a factor of two slower than that of the TI-58C and TI-59. Users were also disappointed by the lack of a solid state software module capability, probably a casualty of the drive for low cost. Page 3 of the TI-66 manual stated "There are no HIR commands or other hidden features on the TI-66 that you may have accessed on the TI-58/58C/59 through illegal key sequences." Nevertheless, Dave Leising, Robert Prins and other users discovered such hidden features as alternate addressing modes, alternate partitioning modes, and hexadecimal codes.

In 1987 Texas Instruments introduced TI-95, with a 31-character alphanumeric display, quasi-QWERTY keyboard, 8K of RAM and a symbolic programming language based on the TI-59 dialect. New commands included hyperbolic functions, calculations with binary and hexadecimal numbers, solving equations, radix conversions, etc. Magnetic cards were replaced by battery backed-up 8K RAM modules. TI-95 was not very successful in the market place.

Today Texas Instruments produces graphing calculators from the TI-8x series. Although significantly different and much more powerful then TI-59, these graphing calculators are build on the success of their predecessors. In them, part of the TI-59 legend lives on...

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