Tag Archives: eprom

EPROM data decay

EPROM short for Erasable Programmable Read-Only Memory is a relict from the early days of computing. It is a from of memory used to store program code for CPU and micro computer. As the name states it is a read-only memory this means that in normal operation the memory content can only be read but not altered. To erase then the memory the chip needs to be exposed to UV light. For this propose the housing of the chip has a built in quartz glass window. I used a so called flash gun which is basically a mains powered fast firing strobe light which is pointed on to the window.

The process of erasing the memory takes some time. I interrupted the erasing process to monitor the progress erasing process by dumping the chips memory into a file. During the first 60 seconds of the chip being exposed to the light no data change occurs. After that the memory fades pretty fast. Even the placement and structure of the memory cells on the chip is somewhat recognizable.

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Initial content

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Reading Flash and EPROM chips and visualizing their contents

This post can be seen as a follow up to my recent post[1] adressing the G540 universal programmer. The reason why I bought this programmer was that I have collected many old memory chips. I was always curious what kind of interesting data they might contain. A EPROM reader was needed and since my urge to build an Arduino shield for that purpose lapsed soon after sourcing some MCP23S17[2] SPI port expander chips.  So I bought the G540 I mentioned before.  Continue reading Reading Flash and EPROM chips and visualizing their contents


  1. My first impression of the Genius G540 universal programmer 
  2. Microchip product page of the MCP23S17