25C040XT-ESLASHST datasheet(10/22 Pages) MICROCHIP

10 / 22 page

25AA040/25LC040/25C040

DS21204E-page 10

3.5

Read Status Register (RDSR)

The RDSR instruction provides access to the STATUS

even during a write cycle. The STATUS register is

formatted as follows:

The Write-In-Process (WIP) bit indicates whether the

25XX040 is busy with a write operation. When set to a

‘1’, a write is in progress, when set to a ‘0’, no write is

in progress. This bit is read-only.

The Write Enable Latch (WEL) bit indicates the status

of the write enable latch. When set to a ‘1’, the latch

allows writes to the array, when set to a ‘0’, the latch

prohibits writes to the array. The state of this bit can

always be updated via the WREN or WRDI commands

regardless of the state of write protection on the

STATUS register. This bit is read-only.

The Block Protection (BP0 and BP1) bits indicate

which blocks are currently write-protected. These bits

are set by the user issuing the WRSR instruction. These

bits are nonvolatile.

See Figure 3-6 for RDSR timing sequence.

3.6

Write Status Register (WRSR)

The WRSR instruction allows the user to select one of

four levels of protection for the array by writing to the

appropriate bits in the STATUS register. The array is

divided up into four segments. The user has the ability

to write-protect none, one, two, or all four of the

segments of the array. The partitioning is controlled as

illustrated in Table 3-2.

See Figure 3-7 for WRSR timing sequence.

TABLE 3-2:

ARRAY PROTECTION

FIGURE 3-6:

READ STATUS REGISTER SEQUENCE

FIGURE 3-7:

WRITE STATUS REGISTER SEQUENCE

7654

XXXX

BP1

BP0

WEL

WIP

BP1

BP0

Array Addresses

Write-Protected

none

upper 1/4

(0180h-01FFh)

upper 1/2

(0100h-01FFh)

all

(0000h-01FFh)

1011

12131415

765

Instruction

Data from STATUS register

High-impedance

SCK

234567

1011

12131415

765

Instruction

Data to STATUS register

High-impedance

SCK

234567

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