Project X


 The landscape of Programmable Pocket Calculators was clearly laid out between 1974 and 1976: Hewlett Packard respected as leader in innovation and marketing their perfectly engineering products in the upper price segment while Texas Instruments following up within roughly one year and appealing a broader market through aggressive pricing. This storyline changed dramatically on May 24, 1977 when Texas Instruments introduced the now legendary TI Programmable 59 and its sibling TI-58, featuring a novelty, the Solid State Software ModulesTM with up to 5,000 program steps. A small lid on the backside of the TI-58/TI-59 allowed for easy access to the modules roughly the size of thumb tip.

The Master Library, known as "Module -1-", with 25 different programs was included with the TI-58 and TI-59. Twelve additional Solid State Software Modules, known as "Module -2- to -13-" were available from Texas Instruments as Standard Libraries. Due to this innovative module concept both the TI-58 and TI-59 gained a lot of attention and dozens of Modules were released for applications ranging from insurance fee calculations to tax calculations to screw joint calculations, HVAC design, pool water analysis and even flight computers for the USMC Harrier.

Understanding the game of cat and mouse with Hewlett Packard, Texas Instruments initiated already in Summer 1977 the "Project X" with clear objectives in mind


• To provide upgrade leadership product to replace TI-59
• Expand concepts of problem solving via calculator device
• Incorporate:
   - State-of-the-art Technologies
   - System Design
   - System Expansion
• To simplify ease of use and provide market expansion among professionals and end users:
   - Technical Professionals
   - Non-Technical Professionals

The ambitious requirements for "Project X" were finalized in January 1978:

• Equation Operating System (EOS)
   - Equation can be entered without execution
   - Display will scroll when full
   - Equation can be edited (Backstep, Insert, Delete)
   - Equation is saved to be executed or repeated with new data
• 16 Character 5*7 dot matrix display
   - Full alphanumeric display
   - Equation trace and prompting in the display
• More flexible user memory
   - Basic memory is 1,000 program steps or 125 data registers with partitioning by the user
   - Solid State Software approach (CROM) has been expanded to include Drop-in RAM (CRAM).
   - CROMs and CRAMs are interchangeable and two slots are available on the calculator
   - Basic memory can be expanded to 3,000 steps of 375 data registers
   - CROMs will be 15,000 program steps, up to 99 programs per CROM, up to 10,000 steps per program

Goal: Define an operating system or "language" for Product X that allows the user to enter problems as they are normally written

• Equation Operating System (EOS)
• More powerful than the TI-59
• Much easier and more obvious to use than the TI-59
• Unary and binary operations will be entered as they are written
   Example: SIN 30 =
• Automatic variable assignment
   Examples: 30 => B  10 => C   SIN B + C => A  (A = 10.5)
• Implied multiplication
   Example: 2A + B = Calculates (2 x A) + B
• Integer powers of variables
   Example: A5 means the value stored in "A" is raised to the 5th power

Or in other words: The capabilities of an SR-60A desktop calculator fitting into the package of a TI-30, operating 150 hours on the charge of a small AA-sized rechargeable battery. It is obvious that this challenging goal could not be realized with the TMC501E building blocks used with the TI-59 and tracing back to the SR-50 introduced already in January 1974 and manufactured with a power hungry PMOS process.

The only existing component reused from the TI-59 is the keyboard which in succession created a lot of headaches with the TI-55-II due to the lower voltages of the new designs (3V versus 16V).

The scope of "Project X" included not only the Programmable Calculator with its CRAM and CROM modules, today known as TI-88, but two additional peripherals connecting with a 2-pin Peripheral I/O connector to the calculator:

• PC-800: Thermal Printer for printing 16 characters per line at 3 lines per second
• CA-800: Cassette Interface for archiving of both programs and data with a tape recorder

with permission of the author