FM25CL64B Ramtron, FM25CL64B Datasheet - Page 5

• Manufacturer Part Number: FM25CL64B
• Description: 3V F-RAM Memory
• Manufacturer: Ramtron

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Data Transfer
All data transfers to and from the FM25CL64B occur
in 8-bit groups. They are synchronized to the clock
signal (SCK), and they transfer most significant bit
(MSB) first. Serial inputs are registered on the rising
edge of SCK. Outputs are driven from the falling
edge of SCK.
Command Structure
There are six commands called op-codes that can be
issued by the bus master to the FM25CL64B. They
are listed in the table below. These op-codes control
the functions performed by the memory. They can be
divided into three categories. First, there are
commands that have no subsequent operations. They
perform a single function such as to enable a write
operation. Second are commands followed by one
byte, either in or out. They operate on the Status
Register. The third group includes commands for
memory transactions followed by address and one or
more bytes of data.
Table 1. Op-code Commands
Rev. 1.2
Feb. 2011
Name
WREN
WRDI
RDSR
WRSR
READ
WRITE
Description
Set Write Enable Latch
Write Disable
Read Status Register
Write Status Register
Read Memory Data
Write Memory Data
Op-code
0000 0110b
0000 0100b
0000 0101b
0000 0001b
0000 0011b
0000 0010b
Figure 5. WREN Bus Configuration
Figure 6. WRDI Bus Configuration
WREN - Set Write Enable Latch
The FM25CL64B will power up with writes disabled.
The WREN command must be issued prior to any
write operation. Sending the WREN op-code will
allow the user to issue subsequent op-codes for write
operations. These include writing the Status Register
(WRSR) and writing the memory (WRITE).
Sending the WREN op-code causes the internal Write
Enable Latch to be set. A flag bit in the Status
Register, called WEL, indicates the state of the latch.
WEL=1
Attempting to write the WEL bit in the Status
Register has no effect on the state of this bit – only
the WREN op-code can set this bit. The WEL bit will
be automatically cleared on the rising edge of /S
following a WRDI, a WRSR, or a WRITE operation.
This prevents further writes to the Status Register or
the F-RAM array without another WREN command.
Figure 5 below illustrates the WREN command bus
configuration.
WRDI - Write Disable
The WRDI command disables all write activity by
clearing the Write Enable Latch. The user can verify
that writes are disabled by reading the WEL bit in the
Status Register and verifying that WEL=0. Figure 6
illustrates the WRDI command bus configuration.
indicates
FM25CL64B - 64Kb 3V SPI F-RAM
that
writes
are
Page 5 of 14
permitted.
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