AT25080/160/320/640

6

Serial Interface Description

MASTER: The device that generates the serial clock.

SLAVE: Because the Serial Clock pin (SCK) is always an

input, the AT25080/160/320/640 always operates as a

slave.

TRANSMITTER/RECEIVER: The AT25080/160/320/640

has separate pins designated for data transmission (SO)

and reception (SI).

MSB: The Most Significant Bit (MSB) is the first bit trans-

mitted 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.

INVALID OP-CODE: If an invalid op-code is received, no

data will be shifted into the AT25080/160/320/640, 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 AT25080/160/320/640 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 out-

put pin (SO) will remain in a high impedance state.

HOLD: The HOLD pin is used in conjunction with the CS

pin to select the AT25080/160/320/640. 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 and WPEN bit is “1”, all write opera-

tions to the status register are inhibited. WP going low

while CS is still low will interrupt a write to the status regis-

ter. If the internal write cycle has already been initiated, WP

going low will have no effect on any write operation to the

status register. The WP pin function is blocked when the

WPEN bit in the status register is "0". This will allow the

user to install the AT25080/160/320/640 in a system with

the WP pin tied to ground and still be able to write to the

status register. All WP pin functions are enabled when the

WPEN bit is set to “1”.

SPI Serial Interface