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I noticed that there were two separate instructions to read data from the data buffer of the W25N01GVxxIG flash chip. There is Read Data(0x13) and Fast Read(0x0B), but their descriptions seem to be the same on the datasheet, except for the fact that the fast read instruction has more dummy clock cycles.

I found a similar question on this website, and the answer for that was that the clock speed was slower for the regular read instruction. That doesn't seem to be the case for this particular chip.

Does anyone know why there are two separate instructions that seem to have the same purpose?

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The fast read allows functions described on pages 41-51. They seem to have allowed the basic read with similar frame as other fast read functions, which doesn't differ from the normal read in other aspects but the communication data frame.

"...allowing equivalent clock rates of 208MHz (104MHz x 2) for Dual I/O and 416MHz (104MHz x 4) for Quad I/O when using the Fast Read Dual/Quad I/O instructions"

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  • \$\begingroup\$ The flash chip runs on the SPI protocol not I2C. But basically what you're saying is that both the instructions are the same except the read frame? \$\endgroup\$ Jan 25, 2022 at 8:14
  • \$\begingroup\$ Sorry, my bad, I meant SPI. You understood the difference for the normal read, the frame is only slightly different, but the dual/quad reads are only available for the "fast read" \$\endgroup\$
    – Ralph
    Jan 25, 2022 at 8:23

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