Connecting the RESET# Signal to IO3/RESET# Signal on S25FL-L, 16-Pin SO and 24-Ball BGA Packages – KBA219553

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Question:

Can the RESET# input signal be connected to the IO3/RESET# input signal on the S25FLxxxL, 16-pin SO and 24-ball BGA package?

 

Answer:

Yes, theoretically, and only for certain use cases; this is not best practice.

Although the RESET# and IO3/RESET# can accomplish the same hardware reset function for certain flash use cases, it is not recommended to connect RESET# with IO3/RESET# for the higher pin count (> 8 pin) packages — even if you will never use the IO3 pin function. For these packages, the best practice is to use the separate, dedicated, RESET# connection.

The multiplexed IO3/RESET# pin warrants a closer look for the 8-pin packages because there is no spare pin for a dedicated RESET# signal when the package is limited to 8 pins.

There are actually two controls shown in the FL-L datasheet (002-12878 Rev B) for the IO3/RESET# pin. The first control in Configuration Register 2 is CR2xV[7] = IO3R:

Setting this bit to 0 disables the multiplexed IO3/RESET# function, so this pin is always IO3 and the RESET# function is always disabled. Setting this bit to 1 enables the multiplexed IO3/RESET# function, so the function of this pin is chosen by the QUAD bit.

The second control is in Configuration Register 1 CR1xV[1] = QUAD:

So, if CR2xV[7] = IO3R = 1, then the multiplexed IO3/RESET# pin has the RESET# function while QUAD=0 and it has the IO3 function when QUAD = 1.