Electrical – IC specification


I am pretty new to this, and I am trying to learn about what specifications I should be looking for when doing a chip replacement.

For example, lets say I know 100% sure my BIOS chip is broken. And I would like to replace this broken chip with a blank chip, which I will later reprogram.

How do it know what empty chip to order on-line, cause there are many different specifications with every chip?

Lets say my original iMac uses this chip: MX25L3205D.

Does it mean that any blank chip which has 25l32 in it can be used?

Best Answer

When doing chip replacements like that, your #1 best bet is to find the exact matching part number and use that.

Barring that, it gets complicated based on the part in question. Using this as an example, we're looking in the general class of SPI flash memory devices. The MX25L3205D is a 32Mbit CMOS Serial Flash. To find a potential replacement, I would look for:

  • Matching pinout (there is a pseudo-standard for SPI memories like this, so you're probably fine)
  • Matching size (32Mbit) and organization (sectors, blocks, etc.)
  • Matching package (PDIP, SOIC, etc.)
  • Matching supply voltage / power requirements
  • Matching command-set (i.e. is 0x06 still WREN. Also kind of a pseudo-standard)
  • A hope that in traditional Apple fashion, this was not a custom chip made for them that has secret authentication / other data on-board

Even after matching all that, there's no guarantee it will work with an alternate -- perhaps the new chip is on a smaller lithography with much, much faster rise/fall times and the PCB layout isn't up to snuff in terms of impedance control or routing (this is a common failure mode for designs that move to die-shrunk SPI/DDR chips after the first design revs).

I bet you could find a compatible part within a hour or so of digging through the usual flash vendors' product lines. No offense though, I might have one of your EE buddies go find it for you in exchange for a six-pack or something.

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