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NM25C040EMT8 Datasheet(PDF) 8 Page - Fairchild Semiconductor |
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NM25C040EMT8 Datasheet(HTML) 8 Page - Fairchild Semiconductor |
8 / 10 page 8 www.fairchildsemi.com NM25C040 Rev. D.1 SCK SI SO CS D0 D1 D2 DS012401-12 Functional Description (Continued) FIGURE 10. Write Sequence The READY/BUSY status of the device can be determined by executing a READ STATUS REGISTER (RDSR) instruction. Bit 0 = 1 indicates that the WRITE cycle is still in progress and Bit 0 = 0 indicates that the WRITE cycle has ended. During the WRITE programming cycle (Bit 0 = 1) only the READ STATUS REGIS- TER instruction is enabled. The NM25C040 is capable of a 4 byte PAGE WRITE operation. 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 address will remain constant. If the master should transmit more than 4 bytes of data, the address counter will “roll over,” and the previously loaded data will be reloaded. See Figure 11. The WRSR command requires the following sequence. The CS line is pulled low to select the device and then the WRSR op-code is transmitted on the SI line followed by the data to be pro- grammed. See Figure 12. CS SI SO Write Op-Code Byte Addr (n) Data (n) Data (n + 1) Data (n + 2) Data (n + 3) CS SI SO WRSR Op-Code SR Data xxxxBP1BP0xx DS012401-13 DS012401-14 FIGURE 11. 4 Byte Page Write FIGURE 12. Write Status Register BP0 SCK SI SO CS DS012401-15 FIGURE 13. Start WRSR Condition 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. Note that the first four bits are don’t care bits followed by BP1 and BP0 then two additional don’t care bits. Programming will start after the CS pin is forced back to a high level. As in the WRITE 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 care bit. See Figure 13. The READY/BUSY status of the device can be determined by executing a READ STATUS REGISTER (RDSR) instruction. Bit 0 = 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. |
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