FM25V02 - 256Kb SPI FRAM
BP0 bits are set to 1, the WPEN bit is set to 1, and
the /W pin is low. This occurs because the block
protect bits prevent writing memory and the /W
signal in hardware prevents altering the block protect
bits (if WPEN is high). Therefore in this condition,
hardware must be involved in allowing a write
operation. The following table summarizes the write
protection conditions.
Table 4. Write Protection
WEL
WPEN
/W
X
X
0
Protected Blocks
Protected
Unprotected Blocks
Protected
Unprotected
Unprotected
Unprotected
Status Register
Protected
0
1
1
1
X
0
Protected
Unprotected
Protected
1
Protected
Protected
1
1
Unprotected
read out for each. Addresses are incremented
internally as long as the bus master continues to issue
clocks. If the last address of 7FFFh is reached, the
counter will roll over to 0000h. Data is read MSB
first. The rising edge of /S terminates a READ op-
code operation and tri-states the Q pin. A read
operation is shown in Figure 10.
Memory Operation
The SPI interface, which is capable of a relatively
high clock frequency, highlights the fast write
capability of the F-RAM technology. Unlike Serial
Flash, the FM25V02 can perform sequential writes at
bus speed. No page buffer is needed and any number
of sequential writes may be performed.
Fast Read Operation
Write Operation
The FM25V02 supports the FAST READ op-code
(0Bh) that is found on Serial Flash devices. It is
implemented for code compatibility with Serial Flash
devices. Following this instruction is a two-byte
address (A14-A0), specifying the address of the first
data byte of the read operation. A dummy byte
follows the address. It inserts one byte of read
latency. The D pin is ignored after the op-code, 2-
byte address, and dummy byte are complete. The bus
master issues 8 clocks, with one bit read out for each.
The Fast Read operation is otherwise the same as an
ordinary READ. If the last address of 7FFFh is
reached, the counter will roll over to 0000h. Data is
read MSB first. The rising edge of /S terminates a
FAST READ op-code operation and tri-states the Q
pin. A Fast Read operation is shown in Figure 11.
All writes to the memory array begin with a WREN
op-code. The next op-code is the WRITE instruction.
This op-code is followed by a two-byte address
value, which specifies the 15-bit address of the first
data byte of the write operation. Subsequent bytes are
data and they are written sequentially. Addresses are
incremented internally as long as the bus master
continues to issue clocks. If the last address of 7FFFh
is reached, the counter will roll over to 0000h. Data is
written MSB first. A write operation is shown in
Figure 9.
Unlike Serial Flash, any number of bytes can be
written sequentially and each byte is written to
memory immediately after it is clocked in (after the
8th clock). The rising edge of /S terminates a WRITE
op-code operation. Asserting /W active in the middle
of a write operation will have no effect until the next
falling edge of /S.
Hold
The FM25V02 and FM25VN02 devices have a
/HOLD pin that can be used to interrupt a serial
operation without aborting it. If the bus master pulls
the /HOLD pin low while C is low, the current
operation will pause. Taking the /HOLD pin high
while C is low will resume an operation. The
transitions of /HOLD must occur while C is low, but
the C and /S pins can toggle during a hold state.
Read Operation
After the falling edge of /S, the bus master can issue
a READ op-code. Following this instruction is a two-
byte address value (A14-A0), specifying the address
of the first data byte of the read operation. After the
op-code and address are complete, the D pin is
ignored. The bus master issues 8 clocks, with one bit
Rev. 2.0
May 2010
Page 7 of 17
RAMTRON [ RAMTRON INTERNATIONAL CORPORATION ]
