25CSM04T-ISLASHCS0668 datasheet(26/55 Pages) MICROCHIP

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25CSM04

DS20005817D-page 26

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7.0

READ SEQUENCES

7.1

Reading from the EEPROM

Reading the EEPROM contents can be done whenever

the device is not in an internal write cycle, as indicated

by the Ready/Busy bit of the STATUS register. To read

the EEPROM, first the CS line is pulled low to select the

device and the READ (03h) instruction is transmitted via

the SI line followed by the 24-bit address to be read.

Address bits A23 through A19 are “don’t care” bits

because they do not fall within the addressable

memory range.

Upon completion of the 24-bit address, any data on the

SI line will be ignored. The data (D7–D0) at the

specified address is then shifted out onto the SO line. If

only one byte is to be read, the CS line should be driven

high after the data are clocked out.

The read sequence can be continued since the byte

address is automatically incremented and data will

continue to be shifted out. When the highest address is

reached, the address counter will “rollover” to the

lowest address (000000h) allowing the entire memory

to be read in one continuous read cycle regardless of

the starting address.

The read sequence can be terminated at any point of

the sequence (drive CS high).

FIGURE 7-1:

READ EEPROM (READ) SEQUENCE

SCK

2 34

567

910 11 12

40 41

00 000 0 1 1

AA A

READ Opcode (03h)

Address Bits A23-A0

XX XX X A

D7 D6 D5 D4 D3 D2 D1 D0 D7 D6

Data Byte 1

MSb

High-Impedance

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