We Celebrate the 30th Anniversary of the TI-59

Dallas (May 24, 1977)  „New Programmable Calculators from Texas Instruments feature Solid State Software Program Libraries. In order to encourage interest in programming and computational problem solving, Texas Instruments introduced a number of new general purpose and specialty calculators...TI Programmable 57 ( with 30,000 transistors -- most powerful single chip calculator ever produced), and the TI Programmable 58 and 59.“

Today - 30 years later - we remember this press release from Texas Instruments and place some milestones around the year 1977 in steps of 5 years:

1967: Texas Instruments invented the Integrated Circuit
1972: Texas Instruments started the calculator business with the formal introduction of the TI-2500 Datamath
1977: Texas Instruments introduced with the TI-59 and its smaller sibling TI-58 the most versatile calculators of that time
1982: A dark year, Texas instruments cancelled the TI-88 project
1987: The powerful TI-95 PROCALC arrived
1992: Texas Instruments leads the upper end of the calculator market with a full line of graphics calculators like the TI-81 and TI-85
1997: The TI-92 introduced Symbolic calculating on handheld devices
2002: Texas Instruments sampled with the PLT-SHH1 a unique graphing calculator based on a PDA (Personal Digital Assistant). 
2007: Starting with the TI-81 sales of Texas Instruments have accumulated to more than 40 million graphing calculators.
   And we are still waiting for the TI-Nspire™ and TI-Nspire™ CAS.

TI-59 Technology

PC-100C_1.jpg (56760 Byte)The TI-59 calculator is difficult to describe. In the year 1977 it marked the top of the programmable handheld-calculators with up to 960 programming steps or 100 user memories, a magnetic card reader, the novel Solid State Software Modules™ and the PC100A alphanumeric printer. On the other hand it was the last development using the powerful and modular TMC0501 calculator architecture. Nowadays it is very difficult to explain an early calculator architecture because all „transistor-count“ limitations were past. But remember Moore’s Law published already in the year 1965 at the beginning of the Integrated Circuits (IC’s) era: Moore predicted that the number of transistors per Integrated Circuit would double every 18 months. He forecast that this trend would continue through 1975. Today we know, Moore's Law has been maintained for far longer, and still holds with a doubling every 12 to 36 month true as we entered the new century.

Pocketronic.jpg (58533 Byte)Simple calculators like the Canon Pocketronic introduced in the year 1970 used three IC’s sporting about 1000 transistors each. The first single-chip calculator circuit TMS1802 integrated the complexity of roughly 5000 transistors in the year 1972 but still featured only four functions. The market asked for higher sophisticated calculators with logarithm, trigonometric functions, user memories and even programmability. But the technology wasn’t available that time to integrate all functions into one circuit. Texas Instruments followed in these early days two different approaches:

The single-chip calculator technology was streamlined to a more universal approach leading to the well known TMS1000 microcomputer family
   introduced with the SR-16 and found later in lots of calculators like the TI-50, TI-55 II and even the TI-88.
The TMC0501 building blocks for scalable scientific calculators introduced with the SR-50 and leading to the TI-59. This TMC0501 architecture
   used minimum a 2 chip design with the Arithmetic chip and the SCOM (scanning read only memory) but was expandable to a maximum of 8 SCOM's,
   additional RAM as program memory for programmable calculators, additional RAM for general purpose registers and even a chip driving a printer.

If we discover current electronic handheld calculators we still find two different architectures:

Single-chip calculators based on a modern microcomputer family, usually Toshiba products.
Microprocessor architectures with external ROM (read only memory), RAM (program and data memory) and display drivers centered around an
   8-bit Z80 microprocessor (TI-81) or a 32-bit MC68000 microprocessor (TI-92).

The next tables describe the calculators leading to the TMC0501 architecture, the calculators using the TMC0501 circuit and some products following the TI-59 calculator.

Before the TMC0501





TI-2500-V1.jpg (33096 Byte) Sept. 1972 TI-2500

The TI-2500 Datamath calculator used with the TMS0119 a derivate of the original TMS1802 "calculator-on-a-chip".

sr-10-v1.jpg (37623 Byte) Nov. 1972 SR-10

With the TMS0120 used in the SR-10 engineers in Dallas added to the 8 digit mantissa a two digit exponent display and created the first scientific calculator. Just to recall, the calculator was named Electronic Slide Rule. 

Ten years of the TMC0501





sr-50.jpg (38175 Byte) Jan. 1974 SR-50

The SR-50 started the era of the TMC0501 based calculators. Using one additional TMC0521 SCOM (scanning read only memory) to the Arithmetic circuit the SR-50 could be called the first „full“ scientific calculator.

sr-51.jpg (43743 Byte) Jan. 1975 SR-51

With the SR-51 Texas Instruments made the first time use of the expandability of the TMC0501 architecture. With two SCOM circuits (TMC0522, 0523) the SR-50 got additional statistical functions plus some conversion constants. 

sr-50a.jpg (39548 Byte) Mar. 1975 SR-50A

The SR-50A put the SR-50 electronics in a simpler housing to reduce manufacturing costs.

sr-51a.jpg (41272 Byte) Jun. 1975 SR-51A

The SR-51A put the SR-51 electronics in a simpler housing to reduce manufacturing costs.

sr-52.jpg (47871 Byte) Sep. 1975 SR-52

The remarkable SR-52 is the direct predecessor of the TI-59 and uses most features of the TMC0501 architecture. A deeper exploration of the calculator shows a TMC0501 Arithmetic chip surrounded with a TMC0524 SCOM, two TMC0561/0562 BROM (bare ROM like a SCOM without the scanning feature necessary for the keyboard), two TMC0599 RAM chips for program and data and finally a TMC0595 controlling the internal magnet card read/writer

sr-56.jpg (43330 Byte) May 1976  SR-56

The SR-56 used again the flexibility of the TMC0501 building blocks and added with the TMC0599 a RAM chip to create a programmable scientific calculator. Under the chargeable battery pack a connector brought some internal signals to the outside world and allowed the use of a PC100 printer/security cradle.  Otherwise it looks similar to the SR-50A using the TMS0537/0538 SCOM circuits.

ti-59.jpg (48317 Byte) May 24,1977 TI-59

The TI-59 eventually put all together ! Supplementary to the architecture found in the SR-52 a second ROM in a removable plastic housing called Solid State Software Module™ was added. While the SCOM and BROM memories store the firmware of the calculator, e.g. the algorithm to calculate the log of a number these modules contain application programs with an overall amount of 5000 steps. Each calculator included one module called Master Library with 25 programs. Beside the 13 Solid State Software Modules available from Texas Instruments a lot of highly specialized modules appeared from third party companies.

ti-58.jpg (49116 Byte) May 24,1977 TI-58

The TI-58 introduced together with the TI-59 removed the magnetic card reader and cut the RAM size in half leading to a maximum of 480 program steps or 60 user memories. At first glance a negligible change because the calculator lost the program like the bigger sibling but you had to type it in hand-operated instead using the card reader! Nevertheless the TI-58 was a big success. Dozens of companies developed Solid State Software Modules™ for the TI-58 and even changed the keyboard to customize the calculator for an application. Get some examples in the last line.

TI-58-Marine.jpg (311084 Byte) 1978 TI-58 Marine Navigation

The TI-58 Marine Navigation combined the TI-58, the "Marine Navigation" Solid State Software Module™ and a DC power supply in a solid wooden box for usage on a boat. 

ti-58c.jpg (48549 Byte) 1979 TI-58C

The TI-58C changed the architecture of the original TI-58 slightly. Removing the old-fashioned TMC0598 RAM’s found in both the TI-58 and TI-59 it introduced a low-power C-MOS RAM connected permanently to the power supply. This resulted in a „Continuous Memory“, even in the off-state the user program and data was stored in the calculator. The TI-58C and TI-59 were produced at least until the year 1983 and gave the TMC0501 architecture a life time of 10 years!   

TI-58-Agrippina.jpg (43446 Byte) TI-58-Allianz.jpg (38986 Byte) TI-58-INCOTAX.jpg (47164 Byte) TI-58-Bossard.jpg (52975 Byte) TI-58-CalQTax.jpg (56479 Byte) TI-58_Simca.jpg (47132 Byte) TI-58-Lloyd.jpg (43502 Byte) TI-58-LVM.jpg (43529 Byte) TI-58-Nordstern.jpg (46039 Byte) TI-58C-PWA.jpg (66760 Byte) TIHarrier.jpg (70116 Byte) TI-58-Victiria.jpg (51961 Byte)


After the TMC0501





TI-88.jpg (43828 Byte) never

The TI-88 was supposed to succeed the TI-59. It was announced early in the year 1982 and attracted many TI-58C/59 owners with its alphanumeric display, thousands of program steps, two interchangeable software modules, printer interface and advanced symbolic language. Unfortunately and without any comment the calculator project was cancelled autumn 1982. Maybe Hewlett Packard's advanced HP41C killed the project. The hardware architecture of the calculator is very interesting and uses a total of three 4-bit single-chip microcontrollers based on the TMS1000 family.

TI-66.jpg (44136 Byte) 1983 TI-66

The TI-66 looks different to the known calculators from Texas Instruments and it is. Today we know that this calculator was designed from first scratch and manufactured by Japanese Toshiba company. Nevertheless the calculator could be called the successor of the TI-58C. The calculator is based on a Toshiba single-chip microcontroller.

TI-95.jpg (59277 Byte) 1987 TI-95

Another remarkable calculator was introduced with the TI-95 PROCALC. A huge alphanumeric display, standard keyboard, 8K of RAM and a symbolic programming language based on the TI-59 dialect  together with interchangeable software cartridges were surrounded with peripheral products like the PC-324 printer. Anyway the calculator failed on the market. The architecture was centered around an 8-bit TMC7000 microcontroller.

TI-81.jpg (53207 Byte) 1990 TI-81

The TI-81 was introduced 13 years after the TI-59 and was the last hope for the advanced calculator line of Texas Instruments. And it worked! They entered the market of Graphics calculators and again proofed true to lead the market. In the year 2000 Texas Instruments sold millions and  millions of the TI-83 Plus. The hardware of the TI-81 is similar to a lot of other products: A 8-bit microprocessor of the Z80 family, a huge ROM of 128k Byte capacity, a RAM of 8k Byte size and a drivers for the LCD display.

TI-92.jpg (89172 Byte) Jan. 1996  TI-92

With the TI-92 Texas Instruments introduced the first Symbolic calculator. From the appearance similar to the TI-95 it outdated competition with the power of a 32-bit MC68000 microprocessor and a perfect user-interface providing even 3-dimensional graphs on a high resolution display.

TI-89.jpg (48439 Byte) 1998 TI-89

The TI-89 proofed the genius of Texas Instruments calculator development true. The power of the TI-92 with the size of a handheld electronic calculator!

PLT-SHH1.jpg (52113 Byte) never

Unfortunately we don't know too much about this unique graphing calculator based on a PDA (Personal Digital Assistant).


Architecture of the TI-59

Texas Instruments published all details of the TI-59 calculator architecture: The patent application US3900722 describes the TMC0501 and the SCOM, US4208720 the SR-56, US 4107782 the SR-60 and US4153937 the TI-59. Fortunately some TI-59 fans combined the schematics of the TI-59 Service Manual with the information discovered in the patent applications.
Sipke de Wal compiled a perfect block diagram of both the calculator itself and the CPU (central processing unit) with all the RAM and ROM chips. On his site you could download all the diagrams of the TI-59.

More information

Dejan Ristanovic maintains a wonderful and informative site featuring the TI-59 and nothing else.
Christopher Westfall tells you all about your First Steps of TI-59 Programming.
Sipke de Wal put the Schematics of the TI-59 on the web.

Missing something ?

One important calculator is missing, the huge programmable desktop calculator SR-60 and its successor SR-60A. Unfortunately we own only the SR-60A and don’t have access to a SR-60. To finish the story I need the TMC05xx designations of all chips inside a SR-60. Dear fellow collector, if you are the happy owner of a SR-60 please do me a favor and contact me via email:

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© Joerg Woerner, April 14, 2002. No reprints without written permission.