FM25160 Datasheet, PDF (6/14 Pages) List of Unclassifed Manufacturers – 16Kb FRAM Serial Memory

Ramtron
RDSR - Read Status Register
The RDSR command allows the bus master to verify
the contents of the Status register. Reading Status
provides information about the current state of the
write protection features. Following the RDSR op-
code, the FM25160 will return one bye with the
contents of the Status register. The Status register is
described in detail in a later section.
Figure 6. RDSR Bus Configuration
FM25160
WRSR – Write Status Register
The WRSR command allows the user to select
certain write protection features by writing a byte to
the Status register. Prior to issuing a WRSR
command, the /WP pin must be high or inactive.
Note that on the FM25160, /WP only prevents
writing to the Status register, not the memory array.
Also prior to sending the WRSR command, the user
must send a WREN command to enable writes. Note
that executing a WRSR command is a write
operation and therefore clears the Write Enable
Latch. The bus configuration of RDSR and WRSR
are shown below.
Figure 7. WRSR Bus Configuration
Status Register & Write Protection
The write protection features of the FM25160 are
multi-tiered. First, a WREN op-code must be issued
prior to any write operation. Assuming that writes are
enabled using WREN, writes to memory are
controlled by the Status register. As described above,
writes to the status register are performed using the
WRSR command and subject to the /WP pin. The
Status register is organized as follows.
Table 2. Status Register
Bit 7
654
Name WPEN 0 0 0
3
2
BP1 BP0
1
0
WEL 0
Bits 0 and 4-6 are fixed at 0 and can not be modified.
Note that the Ready bit in many EEPROMs is
12 May 2000
unnecessary as the FRAM writes in real-time and is
never busy. The WPEN, BP1 and BP0 control write
protection features. They are nonvolatile! The WEL
flag indicates the state of the Write Enable Latch.
Writing the WEL bit in the status register has no
affect.
BP1 and BP0 are memory block write protection
bits. They specify portions of memory that are write
protected as shown in the following table.
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