fm3808 Ramtron Corporation, fm3808 Datasheet - Page 16

• Manufacturer Part Number: fm3808
• Description: 256kb Bytewide Fram W/ Real-time Clock
• Manufacturer: Ramtron Corporation

must remain high for at least the minimum precharge
timing specification. The user dictates the beginning
of this operation since a precharge will not begin until
/CE rises. However, the device has a maximum /CE
low time specification that must be satisfied.
Memory Architecture
FRAM memory internally operates with a read and
restore mechanism. Therefore, each read and write
cycle involves a change of state. The memory
architecture is based on an array of rows and
columns. Each access causes an endurance cycle for
an entire 32-bit row (4 bytes). The memory array is
divided into 32 blocks, each 1Kx8. The 5-upper
address lines decode the block selection as shown in
Figure 6. Data targeted for significantly different
numbers of cycles should be located in separate
blocks since memory rows do not extend across block
boundaries.
Each block of 1Kx8 consists of 256 rows and 4
column address locations. The address lines A0-A7
decode row selection and A8-A9 lines decode column
selection. This scheme facilitates a relatively uniform
distribution of cycles across the rows of a block. By
allowing the address LSBs to decode row selection,
the user avoids applying multiple cycles to the same
row when accessing sequential data. For example,
256 bytes can be accessed sequentially without
accessing the same row twice. In this example, one
cycle would be applied to each row. An entire block
of 1Kx8 can be read or written with only four cycles
applied to each row. Figure 7 illustrates the
organization within a memory block.
Rev. 1.3 (EOL)
Feb. 2006
A0-A7
A9-A8
Figure 7. Row and Column Organization
11b
10b
01b
00b
00h
Figure 6. Address Blocks
01h 02h 03h
Block 31
Block 31
Block 30
Block 30
Block 29
Block 29
Block 28
Block 28
Block 3
Block 3
Block 2
Block 2
Block 1
Block 1
Block 0
Block 0
FCh
FDh
FFFFh
FFFFh
FC00h
FC00h
FBFFh
FBFFh
F800h
F800h
F7FFh
F7FFh
F400h
F400h
F3FFh
F3FFh
F000h
F000h
0FFFh
0FFFh
0C00h
0C00h
0BFFh
0BFFh
0800h
0800h
07FFh
07FFh
0400h
0400h
03FFh
03FFh
0000h
0000h
FEh
FFh
Page 16 of 27
FM3808
A14-A10
00100b
Block 4