Datamath Calculator Museum DCM-50A Sidekick TMS0800 ROM Recorder

When Texas Instruments introduced in September 1973 the TMS0800 Product Family, the corresponding patent applications did not only include a complete program listing for a basic single-chip calculator and complete schematics on transistor level, the US3934233A patent application describes in one chapter a so-called test circuitry of the design. The implementation uses basically some shift registers to read out the 320 program words in a TI-specific test setup. Challenging is the timing of the clock and latch signals for these shift registers, the TMS0800 derives a four-phase clock from its internal clock oscillator and some additional external circuitry is necessary to reconstruct the four phases PHI-1 to PHI-4.

To verify our understanding of the TMS0800 test circuitry, we designed with solderless breadboards our own test setup with two shift registers, one to input a 9-bit ROM Address and one to readout the 11-bit Instruction Register.

We were indeed able to read out the internal ROM of a TMS0801 Chip address-by-address and could compare it, line-by-line, with the program code used by Ken Shirriff's amazing JavaScript Simulator. The breadboard served as proof-of-concept but was not meant to read out all known members of the TMS0800 Product Family, including very rare devices as a TMC0806 from the Exactra 19, a TMS0852 from the TI-150 or an odd TMS0833 from the MBO Expert. Enter DCM-50A Sidekick.

When we developed our DCM-50A (Platform), we put our emphasis not only on Characterization of Single-chip Calculator Circuits, but added features to support the Reverse-engineering of Single-chip Calculator Circuits.

The DCM-50A (Platform) includes various means to enable Reverse-engineering of the TMS0800 Product Family:

All signals are made available on two connectors matching the pinout of the Digilent Digital Discovery™, a combined logic analyzer, protocol analyzer, and pattern generator instrument but can be used with any external instrument compatible with 3.3V or 5V signals.

The DCM-50A Sidekick TMS0800 ROM Recorder is attached to these two connectors and provides the necessary hardware for Recording of ROM Images of all TMS0800 Product Family Members:

The FPGA on the MicroNova Mercury 2 Development Board implements the two shift registers to input a 9-bit ROM Address and readout the 11-bit Instruction Register of the TMS0800 Device-under-Test and an interface to the Arduino Nano Every Microcontroller Board. The user interface of the "TMS0800 ROM Recorder" Software running on the Arduino Nano Every is rather simple: A yellow [ADVANCE] button allows to increment the ROM Address, a blue [SELECT] button displays either the Instruction Register or ROM Address on the three Hexadecimal LED Displays and a red [RESET] button - pressed together with the yellow [ADVANCE] button, resets the ROM Address counter to Zero. The true magic comes into play with the green [AUTO] button, it cycles in less than 5 seconds through all 320 ROM Addresses and records the corresponding Instruction Register contents into an ASCII file.

The Recorded ROM Images of the various members of the TMS0800 Product Family 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, August 18, 2024. No reprints without written permission.