UPD1002

DS00001760B-page 36

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3.5.4.4

JEDEC-ID Read Example

To perform a JEDEC-ID command, the device writes 0x9F into the first byte of the SPI_CMD_BUF and the length of the

transfer is 4 bytes. The device first drops SPI_ROM_CE_N, then 8 bits of the command are clocked out, followed by the

24 bits of dummy bytes (due to the length being set to 4) on the SPI_ROM_DO pin. When the transfer is complete, the

SPI_ROM_CE_N goes high. After the first byte, the data on SPI_ROM_DI is clocked into the SPI_RSP_BUF. At the end

of the command, there are three valid bytes in the SPI_RSP_BUF. In this example, 0xBF, 0x25, 0x8E.

FIGURE 3-10:

SPI ROM JEDEC-ID SEQUENCE

SPI_ROM_CE_N

SPI_ROM_CLK

SPI_ROM_DO

SPI_ROM_DI

8

9F

MSB

HIGH IMPEDANCE

11 12 13 14 15 16

12 3 4

05

7

6

10

9

17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34

BF

25

8E

MSB

MSB