DATAMATH CALCULATOR MUSEUM 
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 TI2500 Datamath • 1977: Texas Instruments introduced with the TI59 and its smaller sibling TI58 the most versatile calculators of that time • 1982: A dark year, Texas instruments cancelled the TI88 project • 1987: The powerful TI95 PROCALC arrived • 1992: Texas Instruments leads the upper end of the calculator market with a full line of graphics calculators like the TI81 and TI85 • 1997: The TI92 introduced Symbolic calculating on handheld devices • 2002: Texas Instruments sampled with the PLTSHH1 a unique graphing calculator based on a PDA (Personal Digital Assistant). • 2007: Starting with the TI81 sales of Texas Instruments have accumulated to more than 40 million graphing calculators. And we are still waiting for the TINspire™ and TINspire™ CAS. 
The TI59 calculator is difficult to describe. In the year 1977 it marked the top of the programmable handheldcalculators 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 „transistorcount“ 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.
Simple calculators like the Canon Pocketronic introduced in the year 1970 used three IC’s sporting about 1000 transistors each. The first singlechip 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 singlechip calculator technology was streamlined to a
more universal approach leading to the well known
TMS1000 microcomputer
family 
If we discover current electronic handheld calculators we still find two different architectures:
• Singlechip 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 8bit Z80 microprocessor (TI81) or a 32bit MC68000 microprocessor (TI92). 
The next tables describe the calculators leading to the TMC0501 architecture, the calculators using the TMC0501 circuit and some products following the TI59 calculator.
Picture 
Introduction 
Name 
Comments 
Sept. 1972  TI2500  The TI2500 Datamath calculator used with the TMS0119 a derivate of the original TMS1802 "calculatoronachip". 

Nov. 1972  SR10 
With the TMS0120 used in the SR10 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. 
Picture 
Introduction 
Name 
Comments 
Jan. 1974  SR50  The SR50 started the era of the TMC0501 based calculators. Using one additional TMC0521 SCOM (scanning read only memory) to the Arithmetic circuit the SR50 could be called the first „full“ scientific calculator. 

Jan. 1975  SR51 
With the SR51 Texas Instruments made the first time use of the expandability of the TMC0501 architecture. With two SCOM circuits (TMC0522, 0523) the SR50 got additional statistical functions plus some conversion constants. 

Mar. 1975  SR50A  The SR50A put the SR50 electronics in a simpler housing to reduce manufacturing costs. 

Jun. 1975  SR51A 
The SR51A put the SR51 electronics in a simpler housing to reduce manufacturing costs. 

Sep. 1975  SR52 
The remarkable SR52 is the direct predecessor of the TI59 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 

May 1976  SR56  The SR56 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 SR50A using the TMS0537/0538 SCOM circuits. 

May 24,1977  TI59  The TI59 eventually put all together ! Supplementary to the architecture found in the SR52 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. 

May 24,1977  TI58 
The TI58 introduced together with the TI59 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 handoperated instead using the card reader! Nevertheless the TI58 was a big success. Dozens of companies developed Solid State Software Modules™ for the TI58 and even changed the keyboard to customize the calculator for an application. Get some examples in the last line. 

1978  TI58 Marine Navigation 
The TI58 Marine Navigation combined the TI58, the "Marine Navigation" Solid State Software Module™ and a DC power supply in a solid wooden box for usage on a boat. 

1979  TI58C  The TI58C changed the architecture of the original TI58 slightly. Removing the oldfashioned TMC0598 RAM’s found in both the TI58 and TI59 it introduced a lowpower CMOS RAM connected permanently to the power supply. This resulted in a „Continuous Memory“, even in the offstate the user program and data was stored in the calculator. The TI58C and TI59 were produced at least until the year 1983 and gave the TMC0501 architecture a life time of 10 years! 

Picture 
Introduction 
Name 
Comments 
never (1982) 
TI88  The TI88 was supposed to succeed the TI59. It was announced early in the year 1982 and attracted many TI58C/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 4bit singlechip microcontrollers based on the TMS1000 family. 

1983  TI66 
The TI66 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 TI58C. The calculator is based on a Toshiba singlechip microcontroller. 

1987  TI95  Another remarkable calculator was introduced with the TI95 PROCALC. A huge alphanumeric display, standard keyboard, 8K of RAM and a symbolic programming language based on the TI59 dialect together with interchangeable software cartridges were surrounded with peripheral products like the PC324 printer. Anyway the calculator failed on the market. The architecture was centered around an 8bit TMC7000 microcontroller. 

1990  TI81  The TI81 was introduced 13 years after the TI59 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 TI83 Plus. The hardware of the TI81 is similar to a lot of other products: A 8bit 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. 

Jan. 1996  TI92  With the TI92 Texas Instruments introduced the first Symbolic calculator. From the appearance similar to the TI95 it outdated competition with the power of a 32bit MC68000 microprocessor and a perfect userinterface providing even 3dimensional graphs on a high resolution display. 

1998  TI89  The TI89 proofed the genius of Texas Instruments calculator development true. The power of the TI92 with the size of a handheld electronic calculator! 

never (2002) 
PLTSHH1  Unfortunately we don't know too much about this unique graphing calculator based on a PDA (Personal Digital Assistant). 
Texas Instruments
published all details of the TI59 calculator architecture: The patent
application US3900722 describes the TMC0501 and the SCOM, US4208720 the
SR56, US 4107782 the SR60 and US4153937 the TI59. Fortunately some TI59 fans
combined the schematics of the TI59 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 TI59.
Dejan
Ristanovic maintains a wonderful and informative site featuring the TI59 and nothing else.
Christopher Westfall tells you all about your First Steps of TI59
Programming.
Sipke de Wal put the Schematics of
the TI59 on the web.
One important calculator is missing, the huge programmable desktop calculator SR60 and its successor SR60A. Unfortunately we own only the SR60A and don’t have access to a SR60. To finish the story I need the TMC05xx designations of all chips inside a SR60. Dear fellow collector, if you are the happy owner of a SR60 please do me a favor and contact me via email: joerg@datamath.org
If you have additions to the above article please email: joerg@datamath.org.
© Joerg Woerner, April 14, 2002. No reprints without written permission.