Datamath Calculator Museum DCM-0500 (Platform)

When Hewlett-Packard formally introduced on January 4^th, 1972 its revolutionary HP-35, it seemed to be far ahead of the four bangers like Bowmar's Model 901B based on Texas Instruments' "calculator-on-a-chip" technology introduced just 3 months earlier with the TMS1802, later rebranded as TMS0102. And Hewlett-Packard indeed designed the HP-35 based on a multi-chip architecture using five separate chips, each with a complexity of around 5,000 transistors comparable to the TMS1802 and manufactured by either Mostek Corp., Carrollton, TX or American Microsystems Inc., Santa Clara, CA. Texas Instruments was no stranger to multi-chip architectures, more or less in parallel with the TMS1802 they worked for Canon on the TMC1813/TMC1814 chipset for their Canola L121F Desktop calculator leading directly into the TMS0200 Building Blocks for Desktop Calculators. They are centered around the TMS0200 Data Chip, TMS0300 ROM (Read-Only Memory) Chip and TMC0400 ROM/Register Chip. But each of the three Chips was encapsulated in a large 40-pin Dual In-line Package (DIP) making them unsuitable for a handheld product.

Being already late, Texas Instruments knew that they needed to be better than their competition and they analyzed the hot-selling HP-35 carefully to identify some weaknesses of its design:

Various teams at Texas Instruments were addressing each of these bullet points and the SR-50 was their answer! The calculator was formally introduced on January 15^th, 1974 and here at the Datamath Calculator Museum we celebrate its groundbreaking architecture defining the TMS0500 Building Blocks for Scientific and Programmable Calculators with this DCM-0500 Platform accordingly! While we considered in Summer 2023 the idea of designing a calculator platform for the TMS0500 Building Blocks similar to the DMC-50A, contacted us a member of the TI-59 Community and shared his misery with us and we changed gears immediately. Learn more about the Birth of the DCM-0500. Breadboarding a fully functional SR-60A might be a retirement project.

With the TMS0500 Building Blocks designed exclusively for Texas Instruments' proprietary applications and never made available to OEM manufacturers, available documentation of their features is rather scarce and the Datamath Calculator Museum is committed to fill this gap with "Data Sheets" for the individual components. The modular approach of the TMS0500 architecture is centered around an Arithmetic Chip and at least one so-called Scanning ROM (Read-Only Memory) Chip necessary for a minimum configuration and expandable with different Peripheral Chips like Magnetic I/O Chip, Multi-Register Chips and Printer/Display Chips. A novelty introduced with the TI Programmable 59 are the Solid State Software Modules™ containing up to 5,000 program steps and inserted into the backside of the calculators. From a technical point of view is most of the calculator functionality defined with the various ROM Chips of the TMS0500 Building Blocks, namely the TMC0520 Scanning ROM, its successor TMC0530 Scanning ROM, TMC0580 Double Scanning ROM, TMC0560 Bare ROM and TMC0540 Customer ROM. To provide enthusiasts as much information as possible about calculators based on the TMC0501 Arithmetic Chip or TMC0501E Enhanced Arithmetic Chip, we developed the DCM-0500 Platform to allow Recording of ROM Images of the Integrated Circuits (ICs) used with these designs.

Reverse-engineering of Calculators

Without official data sheets about the individual products of the TMS0500 Building Blocks available, we not only studied schematics, service manuals and patent applications of different calculators, but utilized the art of reverse-engineering with some of the components used with the calculators. Reverse-engineering of a single component in a product is basically a 4-step approach:

Understanding that a product based on the TMS0500 Building Blocks uses always one Arithmetic Chip but could employ multiple different ROM Chips, we centered the DMC-0500 around a TMS0500 ROM Platform and added various connectors supporting all aspects of reverse-engineering necessary to retrieve the stored Bits and Bytes of these ROM Chips.

Observe: The first step in reverse-engineering of calculators centered around the TMS0500 Building Blocks is accessing the relevant signals within a certain product of interest, we typically use the SR-50 as "Minimum Configuration Calculator" and the TI-58 as "Maximum Configuration Calculator", the SR-51 to explore the use of Constants and the SR-51-II to dig into the undocumented Key Codes for calculators other than the TI-58, TI-58C, and TI-59. Looking closely into the communication between the TMC0501 Arithmetic Chip and TMC0521 Scanning Read-Only Memory used with the SR-50 and SR-50A, you understand that there are four signal groups from interest:

The TMS0500 ROM Platform is providing on the West-Port consequently a 10-pin connector for these 9 signals plus an additional GND pin to wire the respective signals of the calculator under Observation accordingly. A second 8-pin connector at the West-Port provides a DC Voltage to power the calculator connected to the TMS0500 ROM Platform, to allow looking into Power-On behavior of the connected calculator, the DC Voltage is provided either momentarily by the Yellow [CALC] push button or using the Red rocker switch. Additionally the 8-pin connector carries the various voltages used within the Integrated Circuits (ICs) of the TMS0500 Building Blocks, namely V_SS (0 V), V_DD (-10 V) and V_GG (-15.8 V) and connected to the ZIF-Sockets of the TMS0500 ROM Platform.

Observation of the serial IRG and EXT signals is usually performed with a Digital Oscilloscope or Logic Analyzer, here at the Datamath Calculator Musuem we rely on our Hewlett-Packard 54645D Mixed Signal Oscilloscope, Agilent 1672G Logic Analyzer and Digilent Digital Discovery. While these devices are typically connected to modern electronics powered by voltages in the range of 3 Volts to 5 Volts, are the TMS0500 chips manufactured in a 8 um metal gate PMOS process requiring two voltages of -10.0 Volts and -15.8 Volts. The TMS0500 ROM Platform is providing level-shifters to 5 Volts for all PMOS signals connected to the West-Port. Another difficulty observing the serial IRG and EXT signals was introduced with Texas Instruments' desire to keep the pin count of the various ICs as low as possible and engineers chose to combine two functions with the IDLE signal:

To allow an easier synchronization of data capturing with Digital Oscilloscopes or Logic Analyzers includes the TMS0500 ROM Platform a "State Counter" signaling the S0 State of the TMS0501/TMC0501E Chips connected to its East-Port. The 10-pin connector of the North-Port of the TMS0500 ROM Platform labeled "DEBUG INTERACE" is providing three signal groups from the West-Port, the S0 State signal in 5 Volt CMOS Level and an additional GND pin for easy observation of the connected calculator:

Analyze: The second step in reverse-engineering of calculators centered around the TMS0500 Building Blocks is understanding the relevant signals of the component from interest and while both Digital Oscilloscopes and Logic Analyzers are handy tools used in Observation, do they usually lack both functionality and comfort in Analyzing the signals. Looking into the power-up behavior of a SR-50 with an Digital Oscilloscope might be overwhelming, after executing a few instructions to initialize internal registers, the TMC0501/TMS0501E Arithmetic Chip is waiting for a pushed key on the keyboard, effectively generating tens of thousands of serial signals per second. In Software Development for Embedded Microcontroller Architectures one important step is called Debugging and there are different approaches between Trial-and-Error and Test-Bench methodology. One commonly used tool is a "Debugger" that connects to the relevant signal of the Microcontroller and allows "Trigger Conditions", e.g. access to a certain memory location on the Address-Bus or certain data content on the Data-Bus. With the TMS0500 Building Blocks based on a serial Register Processor, we followed an approach to de-serialize the relevant signals into parallel 16-bit words, make them available to an Arduino board and develop "TMS0500 DATA Recorder" Software running on a Arduino DUE simply logged the information from the IRG and EXT signals and the I/O Bus and listing them it in a human readable form in a terminal window. The necessary electronics is connected to the East-Port of the TMS0500 ROM Platform and consist of two modules:

The TMS0500 8-Channel Serial Data Recorder 128-Bit Module is basically and arrangement of eight 16-bit Serial-to-Parallel Shift Registers, for the TMS0500 Building Blocks only six channels are used:

While the TMS0500 Building Blocks uses a digit-serial architecture representing numbers in 16*4 bits are other calculator architectures using different approaches, Hewlett-Packard decided for example with its HP-35 with for a bit-serial architecture representing numbers in 56 bits. The TMS0500 8-Channel Serial Data Recorder 128-Bit Module allows not only for reconfiguration of its 128-Bit Shift Registers into eight 16-Bit channels, four 32-Bit channels, two 64-bit channels or one 128-Bit channel, up to eight of the Modules can be stacked in a piggy-back manner for a combined 1024-Bit Module.

The TMS0500 8-Channel Serial Data Recorder is mounted on top of the TMS0500 8-Channel Serial Data Recorder 128-Bit Module (or stack of multiple 128-Bit Modules) and consists of two components:

Main application on the Arduino DUE is the "TMS0500 DATA Recorder" Software that allows the definition of various trigger conditions for logging IRG and EXT signals and the I/O Bus like "Address Match" and "Data Match" with 0,1,X qualifiers, pre-trigger and post-trigger logging and and storing the information in a human readable form. With this powerful tool we logged for example how the TI-58 accesses its Solid State Software Module when performing a simple "Master Library" function, how a SR-51A is accessing its Constant ROM when converting from inches to millimeters or what values the 16 constants with 13-digit precision used with the computing algorithm of trigonometric functions like sine, cosine, or tangent actually have. The user interface of the "TMS0500 DATA Recorder" Software is rather simple, a 16-position rotary switch selects the desired program, a green [INIT] button starts it and a red [STOP] button resets the system. The "Recording" in the Arduino DUE software includes:

Model: Understanding the TMS0500 Building Blocks gained through intensive Observation and Analysis of the relevant signals and information allows in a third step to create replacements of the individual components of the calculator. With most of the calculator functionality defined with the various ROM Chips of the TMS0500 Building Blocks, our focus is clearly on Recording of ROM Images and the easiest way to access their content is to "Emulate" a TMC0501/TMC0501E Arithmetic Chip while accessing the respective ROMs. The TMS0500 Building Blocks define three different types of ROMs:

To access the information stored during the manufacturing process of the various ROM Chips, the TMC0501/TMC0501 Arithmetic Chips are using the four signal groups mentioned earlier:

The TMC0501/TMC0501E Emulator uses a software approach to stimulate the signals used with the various ROMs using an Arduino Nano Every running different programs selected with a rotary switch, level-shifters from the 5 Volt Outputs of the Arduino microcontroller to the PMOS levels used with the ROMs and a DC/DC converter to provide the voltages used with the TMS0500 Building Blocks, namely V_SS (0 V), V_DD (-10 V) and V_GG (-15.8 V). The user interface of the TMC0501/TMC0501E Emulator is pretty simple, the rotary switch selects one of 3 programs and a blue [PLAY] button starts the program and enables the level-shifters for the various output signals. The "Playlist" in the Arduino Nano Every software includes:

The TMC0501/TMC0501E Emulator is compatible with the West-Port of the TMS0500 ROM Platform and can substitute the physical calculators for the purpose of Recording of ROM Images from its ZIF-Sockets.

Deploy: The TMC0501/TMC0501E Emulator allows to stimulate the various ROMs used with the TMS0500 Building Blocks to reveal their stored information and the TMS0500 8-Channel Serial Data Recorder allows logging of the respective responses of the ROMs. Together with the various ZIF-Sockets provided on the the TMS0500 ROM Platform it just takes some coordinated software running on the two Arduino Platforms for Recording of ROM Images. In the "Deploy Configuration" the Arduino DUE is running the "TMS0500 ROM Recorder" Software not only logging the information from the IRG and EXT signals and the I/O Bus but transcribing them into actual ROM listings including Address and Data information.

The user interface of the "TMS0500 ROM Recorder" Software is rather simple, a 16-position rotary switch selects the desired program, a green [INIT] button starts it and a red [STOP] button resets the system. The "Recording" in the Arduino DUE software includes:

The two Arduino Platforms use a handshake to synchronize their program flow and a typical "Recording Session" consist of just seven steps after connecting the Arduino DUE of the TMS0500 8-Channel Serial Data Recorder to a USB Port of a PC or Laptop and starting a Terminal Program:

Recording of ROM Images

Texas Instrument introduced on January 15^th, 1974 with the SR-50 their first product based on the the TMS0500 Building Blocks for Scientific and Programmable Calculators. The SR-50 used with the TMC0501 Arithmetic Chip and TMC0521 Scanning ROM Chip only the bare minimum of its possibilities but the subsequent introduction of the SR-52 Programmable and the PC-100 Printer Cradle clearly demonstrated the scalability of this groundbreaking architecture. While from a technology point of view the SR-60A Prompting Calculator marked the eclipse of the TMS0500 Building Blocks, was it the TI Programmable 59 that will be remembered for eternity.

With most of the calculator functionality defined with the various ROM Chips of the TMS0500 Building Blocks, our focus hear at the Datamath Calculator Museum is clearly on Recording of ROM Images and the easiest way to access their content is to "Emulate" the TMC0501/TMC0501E Arithmetic Chip while accessing the respective ROMs. The TMS0500 Building Blocks define three different types of ROMs:

In 1965, Gordon E. Moore - co-founder of Intel - postulated that the number of transistors that can be packed into a given unit of space will double about every two years. This allowed to integrate more and more transistors, diodes and resistors into Integrated Circuits and consequently the capacity of the ROMs changed over time:

The ROM (Read-Only Memory) Chips used within the TMS0500 Building Blocks are manufactured with an 8 um (early designs) or 6 um (later designs) metal gate PMOS process where the information in the form of the individual Bits that make up a 13-bit Instruction Word, a 2-digit BCD Key Code (8-bit) or 16-digit Constants (64-bit) are stored in the layout of the Chips using a single metal mask. Decapping the chips and photographing them under a microscope makes the individual Bits actually visible and with some additional smart software tools the data content can be retrieved. One of the disadvantages of this brute force method is its destructive character, hence did we develop here at the Datamath Calculator Museum with the DCM0500 Platform an approach to Record the stored ROM Images electronically.

The DCM-0500 Platform is designed with individual modules that can be configured and customized for different purposes, for the Recording of ROM Images we use the "Deploy Configuration" with four modules:

The Recorded ROM Images of the various ROM Chips used within the TMS0500 Building Blocks for Scientific and Programmable Calculators are published as TXT-Files in the "ROM Content" sections of their respective "Data Sheets":

IMPORTANT NOTE: This information is provided as a service of the Datamath Calculator Museum to enthusiasts of early Texas Instruments calculators and please be aware that the Copyright of the Software transcribed in the ROM Images, the underlying algorithm or application might be owned by Texas Instruments or other third parties. The commercial use of the published Recorded ROM Images is strictly prohibited. In case of questions please contact us using the email address listed in the footer of this webpage.

If you have additions to the above article please email: joerg@datamath.org.

© Joerg Woerner, January 15, 2024. No reprints without written permission.