CAT25640

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6

WRITE OPERATIONS

The CAT25640 device powers up into a write disable

state. The device contains a Write Enable Latch (WEL)

which must be set before attempting to write to the memory

array or to the status register. In addition, the address of the

memory location(s) to be written must be outside the

protected area, as defined by BP0 and BP1 bits from the

status register.

Write Enable and Write Disable

The internal Write Enable Latch and the corresponding

Status Register WEL bit are set by sending the WREN

instruction to the CAT25640. Care must be taken to take the

CS input high after the WREN instruction, as otherwise the

Write Enable Latch will not be properly set. WREN timing

is illustrated in Figure 3. The WREN instruction must be

sent prior to any WRITE or WRSR instruction.

The internal write enable latch is reset by sending the

WRDI instruction as shown in Figure 4. Disabling write

operations by resetting the WEL bit, will protect the device

against inadvertent writes.

Figure 3. WREN Timing

SCK

SI

SO

00

0

0

0

11

0

HIGH IMPEDANCE

Dashed Line = mode (1, 1)

CS

Figure 4. WRDI Timing

SCK

SI

SO

0

0

000

10

0

HIGH IMPEDANCE

Dashed Line = mode (1, 1)

CS