Is it possible to define (using only visual inspection of PCB and multimeter) whether or not SPI Flash memory can be properly programmed keeping the device In-circuit, without desoldering IC from the PCB? Or this can be found only via trial and error method? CPU specification is not available.

PCB image 1 and 2 (SPI Flash memory marked "U42")

1 Answer 1


It may be possible. Based on the data sheet you posted, you need to see if Pin 9 is tied directly to ground, or can be controlled by the CPU. If it can be controlled, the chip can be re-programmed.

If Pin 9 is tied to the CPU, you may then be in the realm of trial-and-error to see how to control that pin.

  • It looks there is a resistor after Pin 9. It's not clear whether it controlled by the CPU or grounded.
    – Lexx Luxx
    Jul 23, 2014 at 10:29
  • From the pictures, the resistor does not appear to be grounded. It's probably a pull-up (i.e., write-protect is disabled).
    – devttys0
    Jul 23, 2014 at 14:01
  • So is it possible to program this flash using In-circuit method, without desoldering it from the PCB?
    – Lexx Luxx
    Jul 23, 2014 at 19:40
  • You don't want to go based strictly on what you can see. Your eyes can jump traces. There may also be hidden traces in the PCB. In fact, the resister appears to connect to a VIA (the little hole through the PCB) which often indicates a multi-layer PCB. Use a multi-meter to test connectivity. A resister may also tie it to the cpu. It is hard to tell from the picture.
    – Elros
    Jul 24, 2014 at 13:28
  • As for whether it is possible, it probably is. However, you will need the software on the cpu to actually do it.
    – Elros
    Jul 24, 2014 at 13:46

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