AT25010/020/040

6

Serial Interface Description

MASTER:

The device that generates the serial clock.

SLAVE:

Because the Serial Clock pin (SCK) is always an

input, the AT25010/020/040 always operates as a slave.

TRANSMITTER/RECEIVER:

The AT25010/020/040 has

separate pins designated for data transmission (SO) and

reception (SI).

MSB:

The Most Significant Bit (MSB) is the first bit

transmitted and received.

SERIAL OP-CODE:

After the device is selected with CS

going low, the first byte will be received. This byte contains

the op-code that defines the operations to be performed.

The op-code also contains address bit A8 in both the

READ and WRITE instructions.

INVALID OP-CODE:

If an invalid op-code is received, no

data will be shifted into the AT25010/020/040, and the

serial output pin (SO) will remain in a high impedance state

until the falling edge of CS is detected again. This will reini-

tialize the serial communication.

CHIP SELECT:

The AT25010/020/040 is selected when

the CS pin is low. When the device is not selected, data will

not be accepted via the SI pin, and the serial output pin

(SO) will remain in a high impedance state.

HOLD:

The HOLD pin is used in conjunction with the CS

pin to select the AT25010/020/040. When the device is

selected and a serial sequence is underway, HOLD can be

used to pause the serial communication with the master

device without resetting the serial sequence. To pause, the

HOLD pin must be brought low while the SCK pin is low. To

resume serial communication, the HOLD pin is brought

high while the SCK pin is low (SCK may still toggle during

HOLD). Inputs to the SI pin will be ignored while the SO pin

is in the high impedance state.

WRITE PROTECT:

The write protect pin (WP) will allow

normal read/write operations when held high. When the

WP pin is brought low, all write operations are inhibited.

WP going low while CS is still low will interrupt a write to the

AT25010/020/040. If the internal write cycle has already

been initiated, WP going low will have no effect on any

write operation.

SPI Serial Interface