M95640-W M95640-R M95640-DF
Operating features
The Hold condition ends when the Hold (HOLD) signal is driven high when Serial Clock (C)
is already low.
Figure 6 also shows what happens if the rising and falling edges are not timed to coincide
with Serial Clock (C) being low.
5.4
5.5
Status Register
The Status Register contains a number of status and control bits that can be read or set (as
appropriate) by specific instructions. See Section 6.3: Read Status Register (RDSR) for a
detailed description of the Status Register bits.
Data protection and protocol control
The device features the following data protection mechanisms:
●
Before accepting the execution of the Write and Write Status Register instructions, the
device checks whether the number of clock pulses comprised in the instructions is a
multiple of eight.
●
●
●
All instructions that modify data must be preceded by a Write Enable (WREN)
instruction to set the Write Enable Latch (WEL) bit.
The Block Protect (BP1, BP0) bits in the Status Register are used to configure part of
the memory as read-only.
The Write Protect (W) signal is used to protect the Block Protect (BP1, BP0) bits in the
Status Register.
For any instruction to be accepted, and executed, Chip Select (S) must be driven high after
the rising edge of Serial Clock (C) for the last bit of the instruction, and before the next rising
edge of Serial Clock (C).
Two points should be noted in the previous sentence:
●
The “last bit of the instruction” can be the eighth bit of the instruction code, or the eighth
bit of a data byte, depending on the instruction (except for Read Status Register
(RDSR) and Read (READ) instructions).
●
The “next rising edge of Serial Clock (C)” might (or might not) be the next bus
transaction for some other device on the SPI bus.
Table 2.
Write-protected block size
Status Register bits
Protected block
Protected array addresses
BP1
BP0
0
0
1
1
0
1
0
1
none
none
Upper quarter
Upper half
1800h - 1FFFh
1000h - 1FFFh
0000h - 1FFFh
Whole memory
Doc ID 16877 Rev 16
15/47
STMICROELECTRONICS [ ST ]
