M95010-RBN3TSLASHW datasheet(14/37 Pages) STMICROELECTRONICS

14 / 37 page

M95040, M95020, M95010

14/37

Read Status Register (RDSR)

One of the major uses of this instruction is to allow

the MCU to poll the state of the Write In Progress

(WIP) bit. This is needed because the device will

not accept further WRITE or WRSR instructions

when the previous Write cycle is not yet finished.

As shown in Figure 10., to send this instruction to

the device, Chip Select (S) is first driven Low. The

bits of the instruction byte are then shifted in, on

Serial Data Input (D). The current state of the bits

in the Status Register is shifted out, on Serial Data

Out (Q). The Read Cycle is terminated by driving

Chip Select (S) High.

The Status Register may be read at any time, even

during a Write cycle (whether it be to the memory

area or to the Status Register). All bits of the Sta-

tus Register remain valid, and can be read using

the RDSR instruction. However, during the current

Write cycle, the values of the non-volatile bits

(BP0, BP1) become frozen at a constant value.

The updated value of these bits becomes avail-

able when a new RDSR instruction is executed, af-

ter completion of the Write cycle. On the other

hand, the two read-only bits (Write Enable Latch

(WEL), Write In Progress (WIP)) are dynamically

updated during the on-going Write cycle.

The status and control bits of the Status Register

are as follows:

WIP bit. The Write In Progress (WIP) bit indicates

whether the memory is busy with a Write or Write

Status Register cycle. When set to 1, such a cycle

is in progress, when reset to 0 no such cycle is in

progress.

WEL bit. The Write Enable Latch (WEL) bit indi-

cates the status of the internal Write Enable Latch.

When set to 1 the internal Write Enable Latch is

set, when set to 0 the internal Write Enable Latch

is reset and no Write or Write Status Register in-

struction is accepted.

BP1, BP0 bits. The Block Protect (BP1, BP0) bits

are non-volatile. They define the size of the area to

be software protected against Write instructions.

These bits are written with the Write Status Regis-

ter (WRSR) instruction. When one or both of the

Block Protect (BP1, BP0) bits is set to 1, the rele-

vant memory area (as defined in Table 4.) be-

comes

protected

against

Write

(WRITE)

instructions. The Block Protect (BP1, BP0) bits

can be written provided that the Hardware Protect-

ed mode has not been set.

Figure 10. Read Status Register (RDSR) Sequence

3456789 10 11 12 13 14 15

Instruction

AI01444D

6543210

Status Register Out

High Impedance

MSB

6543210

Status Register Out

MSB

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