5

AT25080A/160A/320A/640A

5082B–SEEPR–1/05

Serial Interface

Description

MASTER: The device that generates the serial clock.

SLAVE: Beca use t he ser i al clo ck pin ( S CK) is alwa ys an input , the

AT25080A/160A/320A/640A always operates as a slave.

TRANSMITTER/RECEIVER: The AT25080A/160A/320A/640A has separate pins des-

ignated 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.

INVALID OP-CODE: If an invalid op-code is received, no data will be shifted into the

AT25080A/160A/320A/640A, and the serial output pin (SO) will remain in a high imped-

ance state until the falling edge of CS is detected again. This will reinitialize the serial

communication.

CHIP SELECT: The AT25080A/160A/320A/640A 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 con ju nction w ith t he CS pin to select th e

AT25080A/160A/320A/640A. 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 register. 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 AT25080A/160A/320A/640A 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”.