FM25C040 Fairchild Semiconductor, FM25C040 Datasheet - Page 8

• Manufacturer Part Number: FM25C040
• Description: 4K-Bit SPI Interface Serial CMOS EEPROM
• Manufacturer: Fairchild Semiconductor

FM25C040U Rev. B
The RDSR command requires the following sequence. The /CS
pin is pulled low to select the EEPROM and then the RDSR
opcode is transmitted on the SI pin. After this is done, data on the
SI pin becomes don’t care. The data from the Status Register is
then shifted out on the SO pin starting with D7 bit first and D0 last.
See Figure 6.
FIGURE 6. Read Status Register
/CS
WRITE ENABLE (WREN):
When V
disabled state. Therefore, all programming modes (Write to memory
array and Status register), must be preceded by a WRITE EN-
ABLE (WREN) instruction. See Figure 7.
FIGURE 7. Write Enable
WRITE DISABLE (WRDI):
Executing this instruction disables all programming modes (Write
to memory array and Status register), preventing the EEPROM
from accidental writes. Once WRDI instruction is executed,
WREN instruction should be executed to re-enable all program-
ming modes. See Figure 8.
FIGURE 8. Write Disable
WRITE SEQUENCE (WRITE):
Write to the array is enabled only when /WP pin is held high and
the EEPROM is write enabled previously (via WREN instruction).
Also, the address of the memory location(s) to be programmed
must be outside the protected address field selected by the Block
Write Protection Level. See Table 4.
/CS
SO
SO
SI
/CS
SO
SI
SI
CC
is applied to the EEPROM, it “powers up” in a write-
OP-CODE
RDSR
WREN Op-Code
WRDI Op-Code
RDSR DATA
8
TABLE 4. Block Write Protection Levels
A WRITE command requires the following sequence. The /CS pin
is pulled low to select the EEPROM, then the WRITE opcode is
transmitted on the SI pin followed by the byte address (A7-A0) and
followed by the data (D7-D0) to be written. See Figure 9 .
FIGURE 9. Byte Write
Internally, the programming will start after the /CS pin is brought
back to a high level. Note that the LOW to HIGH transition of the
/CS pin must occur during the SCK low time immediately after
clocking in the D0 data bit. See Figure 10.
FIGURE 10. Start of Programming
Programming status (Busy/Ready) of the EEPROM can be deter-
mined by executing a READ STATUS REGISTER (RDSR) in-
struction after a write command. Upon executing the RDSR
instruction, if Bit 0 of the RDSR data is “1”, it indicates the WRITE
cycle is still in progress. If it is “0” then the WRITE cycle has ended.
Note that while the internal programming is still in progress (Bit 0
= 1), only the RDSR instruction is enabled. It is recommended that
no other instruction be issued till the internal programming is
complete.
Level
SCK
/CS
0
1
2
3
SO
SI
/CS
SO
SI
D2
Op-Code
Status Register Bits
Write
D1
BP1
0
0
1
1
High Z
Addr
Byte
High Z
D0
Data
BP0
0
1
0
1
Start of internal
programming
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Protected
Address
180-1FF
100-1FF
000-1FF
Array
None