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How to crack 74ls48 ic

How to crack 74ls48 ic

Overview of the 74LS48 chip

The 74LS48 is an 8-bit binary BCD to 7-segment decoder IC chip manufactured by various companies. It converts a binary coded decimal (BCD) number into a decimal digit that can be displayed on a 7-segment display.

Some key features of the 74LS48:

  • Supply voltage: 2V to 6V
  • Decodes 4-bit binary input into 1-out-of-10 decoded outputs
  • Open collector outputs can sink up to 25mA current
  • Typical propagation delay: 15ns

This chip is commonly used in digital clocks, electronic meters, calculators and other embedded systems that need to display numeric information.

Steps to crack the 74LS48

Cracking the 74LS48 means reverse engineering its internal circuitry and logic functions. Here are the key steps involved:

1. Desolder the chip from the PCB

  • Use a desoldering pump or solder wick to remove the chip from the PCB it’s mounted on.
  • Gently apply heat to each pin while slowly lifting the chip. Be careful not to overheat and damage the chip.

2. Chemically remove the plastic packaging

  • The plastic epoxy packaging needs to be dissolved to expose the silicon die inside.
  • Submerge the chip in nitric acid (HNO3) for several hours. The plastic will dissolve leaving just the silicon die.
  • Rinse the die carefully with deionized water and dry.

3. Study the die under a microscope

  • Use a microscope or magnifying glass to visually inspect the tiny structures etched on the silicon.
  • Locate the metal connection layers, transistor arrays, logic gates etc.
  • Compare with the chip’s datasheet diagram to identify functional blocks.

4. Trace the internal connections

  • Use a multimeter in continuity testing mode to trace connections between pins and internal circuit blocks.
  • Probe different test points while toggling input pins to map the internal logic.
  • Draw a schematic diagram showing the identified internal connections.

5. Analyze and characterize the logic functionality

  • Connect input pins to a signal generator to simulate different logic states.
  • Observe the corresponding output pin behavior and note down truth tables.
  • Figure out the underlying logic gates (AND, OR, NOT etc.) used internally.
  • Confirm that the logic matches the functional description in the datasheet.

Conclusion

With some simple tools, patience and an analytical mindset, it is possible to delayer, map and understand the internal circuitry of a microchip like the 74LS48 BCD decoder. This helps gain valuable insights into its inner workings and logic functionality. The process can be repeated for other ICs as well.

Frequently Asked Questions

1. What tools are required to crack an IC?

Desoldering equipment, nitric acid, deionized water, microscope, multimeter, signal generator, tweezers and probes are the basic tools needed. A fume hood is recommended when using acids.

2. How long does it take to crack an IC?

It can take anywhere from a few hours to several days depending on the complexity of the chip. Simple logic ICs with a few hundred transistors can be analyzed in hours, while a microcontroller may take days.

3. Is IC cracking legal?

Reverse engineering chips may violate copyrights or patent protections in some cases. It’s best to consult an attorney about the legal implications. In most cases, cracking for academic research or personal education is allowed.

4. What precautions should be taken?

  • Use protective gear like goggles, gloves and mask when handling acids or other dangerous chemicals.
  • Work in a well ventilated area to avoid inhaling toxic fumes.
  • Handle the chip with care using anti-static precautions to avoid ESD damage.
  • Properly dispose waste acids, solvents, etc.

5. Can a cracked IC be reused?

Unfortunately, the IC will no longer function after being chemically delayered. The process is destructive and irreversible. Only a bare silicon die remains that cannot be reassembled into a working chip.