FM28V020 - 32Kx8 F-RAM

Document Number: 001-86204 Rev. *A

Page 5 of 16

access. Precharge is user-initiated by driving at least

one of the chip enable signals to an inactive state. The

chip enable must remain inactive for at least the

Precharge is also activated by changing the upper

addess A(14:3). The current row is first closed prior

to accessing the new row. The device automatically

detects an upper order address change which starts a

precharge operation, the new address is latched, and

access time. Refer to the Read Cycle Timing 1

diagram on page 9. Likewise a similar sequence

occurs for write cycles. Refer to the Write Cycle

Timing 3 diagram on page 11.

The rate at which

respectively.

Endurance

The FM28V020 is capable of being accessed at least

10

operates

with

a

read

and

restore

mechanism.

Therefore, an endurance cycle is applied on a row

basis. The F-RAM architecture is based on an array

of rows and columns. Rows are defined by A14-A3

and column addresses by A2-A0. The array is

organized as 4K rows of 8-bytes each. The entire row

is internally accessed once whether a single byte or

all eight bytes are read or written. Each byte in the

row is counted only once in an endurance calculation

if the addressing is contiguous in nature.

The user may choose to store CPU instructions and

run them from a certain address space. The table

below shows endurance calculations for 256-byte

repeating loop, which includes a starting address and

initial access, 7 page mode accesses, and a CE

precharge. The number of bus clocks needed to

complete an 8-byte read transaction is 1+7+1 or 9

clocks.

The

entire

loop

causes

each byte to

experience only one endurance cycle. F-RAM read

and write endurance is virtually unlimited.

Table 1. Time to Reach 100 Trillion Cycles for Repeating 256-byte Loop

Bus Freq

(MHz)

Bus Cycle

Time (ns)

256-byte

Transaction

Time ( s)

Endurance

Cycles/sec.

Endurance

Cycles/year

Years to

Reach 10

14

Cycles

10

100

28.8

34,720

1.09 x 10

12

91.7

5

200

57.6

17,360

5.47 x 10

11

182.8