Serial Interface Description

MASTER:

The device that generates the serial clock.

SLAVE:

Because the Serial Clock pin (SCK) is always

an input, the AT25128 always operates as a slave.

TRANSMITTER/RECEIVER: The

A T 2 5128

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.

INVALID OP-CODE:

If an invalid op-code is received,

no data will be shifted into the AT25128, and the serial

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

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

ize the serial communication.

CHIP SELECT:

The AT25128 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 AT25128. 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 reg-

ister. 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 AT25128 in a system with the WP pin

tied to ground and still be able to write to the status regis-

ter. All WP pin functions are enabled when the WPEN bit

is set to “1".

SPI Serial Interface

6

AT25128