83Redux: Part One – A Journey into the TI83 Plus Graphing Calculator

Screenshot 2023-02-12 at 11.53.40 AM

As a maker and designer with a passion for understanding the inner workings of technology, I was excited to get my hands on a TI83 Plus graphing calculator. This popular device, produced by Texas Instruments, has been a staple in classrooms and offices for over two decades, and I was eager to uncover the secrets hidden within its circuit board.

So, I set out on a journey to reverse engineer the TI83 Plus, to gain a deeper understanding of its design and functionality. My goal was to document the process, share my findings, and hopefully inspire others to explore the world of reverse engineering.

The device I was presented with was marked ‘TI 83(A)’ and ‘9TA83ADMB-31G’. The board appears to be a revision A model.

According to Texas Instruments, this calculator was designed to use a Zilog Z80 MCU operating at 6 MHz, but upon initial inspection, I was surprised to find that the device was actually using a custom ASIC marked ‘INVENTEC 6SI837 0A JAPAN 0209EAI’. This was a mystery to me, as no information or datasheets were readily available for this MCU.

Despite this unexpected finding, I was determined to continue my reverse engineering journey. The device had some cosmetic damage, likely caused by battery corrosion, but all components appeared to be intact. With my trusty tools in hand, I began to take the calculator apart, piece by piece.

As I delved deeper into the device, I discovered some fascinating design choices and trade-offs. For example, the calculator was designed to use two different levels of flash memory modules, which was a clever solution to potential part shortages.

I also found that the IO jack on the bottom of the device had oversized copper pads to help overcome any damage caused by the insertion force of the IO cable. This was a small detail, but it showed the manufacturer’s attention to detail and commitment to delivering a high-quality product.

Over the coming weeks and months, I’ll be sharing more of my findings in a series of blog posts. I’ll go over the different subsystems of the calculator in depth and show you some of the pictures I took along the way. Whether you’re an engineer, student, or just interested in technology, I hope these posts will inspire you to explore the world of reverse engineering and gain a deeper understanding of the devices that surround us.

In the meantime, stay tuned for the next installment of my journey into the TI83 Plus.

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