NM25C040 データシートの表示（PDF） - Fairchild Semiconductor

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NM25C040

4K-Bit Serial CMOS EEPROM (Serial Peripheral Interface (SPI) Synchronous Bus)

Fairchild Semiconductor 

Functional Description (Continued)

FIGURE 10. Write Sequence

The WRSR command requires the following sequence. The CS

line is pulled low to select the device and then the WRSR op-code

CS

is transmitted on the SI line followed by the data to be pro-

 grammed. See Figure 12.

FIGURE 12. Write Status Register

SCK

CS

SI D2

D1

D0

SI

SO

DS012401-12

The READY/BUSY status of the device can be determined by

SO

WRSR

SR Data

Op-Code xxxxBP1BP0xx

DS012401-14

executing a READ STATUS REGISTER (RDSR) instruction. Bit 0

= 1 indicates that the WRITE cycle is still in progress and Bit 0 = Note that the first four bits are don’t care bits followed by BP1 and

0 indicates that the WRITE cycle has ended. During the WRITE BP0 then two additional don’t care bits. Programming will start

programming cycle (Bit 0 = 1) only the READ STATUS REGIS- after the CS pin is forced back to a high level. As in the WRITE

TER instruction is enabled.

instruction the LOW to HIGH transition of the CS pin must occur

during the SCK low time immediately after clocking in the last don’t

The NM25C040 is capable of a 4 byte PAGE WRITE operation. care bit. See Figure 13.

After receipt of each byte of data the two low order address bits are

internally incremented by one. The seven high order bits of the

FIGURE 13. Start WRSR Condition

address will remain constant. If the master should transmit more

than 4 bytes of data, the address counter will “roll over,” and the

CS

 previously loaded data will be reloaded. See Figure 11.

FIGURE 11. 4 Byte Page Write

CS

Write

Byte

Data

Data

Data

Data

SI

Op-Code Addr (n) (n)

(n + 1) (n + 2) (n + 3)

SO

SCK

SI

BP0

SO

DS012401-15

The READY/BUSY status of the device can be determined by

executing a READ STATUS REGISTER (RDSR) instruction. Bit 0

DS012401-13 = 1 indicates that the WRSR cycle is still in progress and Bit 0 =

0 indicates that the WRSR cycle has ended.

At the completion of a WRITE cycle the device is automatically

returned to the write disable state.

At the completion of a WRITE cycle the device is automatically

returned to the write disable state.

If the device is not WRITE enabled, the device will ignore the

WRITE instruction and return to the standby state when CS is

forced high. A new CS falling edge is required to re-initialize the

serial communication.

WRITE STATUS REGISTER (WRSR): The WRITE STATUS

REGISTER (WRSR) instruction is used to program the non-

volatile status register Bits 2 and 3 (BP0 and BP1). The WRITE

PROTECT (WP) pin must be held high and two separate instruc-

tions must be executed. The chip must first be write enabled via

the WRITE ENABLE instruction and then a WRSR instruction

must be executed.

NM25C040 Rev. D.1

8

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