S25FS256S datasheet(76/154 Pages) SPANSION

76 / 154 page

S25FS-S Family

S25FS-S_00_04 November 6, 2013

Data

Sheet

(Pre limin ar y)

Data Protection

9.1

Secure Silicon Region (OTP)

The device has a 1024 byte One-Time Program (OTP) address space that is separate from the main flash

array. The OTP area is divided into 32, individually lockable, 32-byte aligned and length regions.

The OTP memory space is intended for increased system security. OTP values can “mate” a flash

component with the system CPU/ASIC to prevent device substitution. See OTP Address Space on page 58,

OTP Program (OTPP 42h) on page 123, and OTP Read (OTPR 4Bh) on page 123.

9.1.1

Reading OTP Memory Space

The OTP Read command uses the same protocol as Fast Read. OTP Read operations outside the valid 1-kB

OTP address range will yield indeterminate data.

9.1.2

Programming OTP Memory Space

The protocol of the OTP programming command is the same as Page Program. The OTP Program command

can be issued multiple times to any given OTP address, but this address space can never be erased.

The valid address range for OTP Program is depicted in Figure 8.1, OTP Address Space on page 58. OTP

Program operations outside the valid OTP address range will be ignored, without P_ERR in SR1V set to 1.

OTP Program operations within the valid OTP address range, while FREEZE = 1, will fail with P_ERR in

SR1V set to 1. The OTP address space is not protected by the selection of an ASP Protection mode. The

Freeze bit (CR1V[0]) may be used to protect the OTP Address Space.

9.1.3

Spansion Programmed Random Number

Spansion standard practice is to program the low order 16 bytes of the OTP memory space (locations 0x0 to

0xF) with a 128-bit random number using the Linear Congruential Random Number Method. The seed value

for the algorithm is a random number concatenated with the day and time of tester insertion.

9.1.4

Lock Bytes

The LSB of each Lock byte protects the lowest address region related to the byte, the MSB protects the

highest address region related to the byte. The next higher address byte similarly protects the next higher 8

regions. The LSB bit of the lowest address Lock Byte protects the higher address 16 bytes of the lowest

address region. In other words, the LSB of location 0x10 protects all the Lock Bytes and RFU bytes in the

lowest address region from further programming. See OTP Address Space on page 58.

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