1. This parameter is characterized and is not 100% tested. Contact Atmel for further information.
Serial Interface Description
MASTER: The device that generates the serial clock.
SLAVE: Because the serial clock pin (SCK) is always an input, the AT25128B/256B always operates as a slave.
TRANSMITTER/RECEIVER: The AT25128B/256B has separate pins designated for data transmission (SO) and
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 con-
tains 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 AT25128B/256B, and the
serial output pin (SO) will remain in a high impedance state until the falling edge of CS is detected again. This will
reinitialize the serial communication.
CHIP SELECT: The AT25128B/256B 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 AT25128B/256B. When the device is
selected and a serial sequence is underway, HOLD can be used to pause the serial communication with the mas-
ter 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 operations 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 AT25128B/256B 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”.
HOLD to Output Low Z
HOLD to Output High Z
Output Disable Time
Write Cycle Time
3.3V, 25°C, Page Mode
AC Characteristics (Continued)
Applicable over recommended operating range from T
A = – 40°C to + 85°C, VCC = As Specified,
CL = 1 TTL Gate and 30 pF (unless otherwise noted)