Because the Serial Clock (SCK) pin is always an input, the AT25320B/AT25640B always operates as a client.
Transmitter/receiver:
The AT25320B/AT25640B 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 Opcode:
After the device is selected with CS going low, the
first byte will be received. This byte contains the opcode that defines the
operations to be performed.
Invalid Opcode:
If an invalid opcode is received, no data will be shifted into the AT25320B/AT25640B, and the Serial Output (SO) pin
will remain in a high‑impedance state until the falling edge of
CS is detected again. This will reinitialize
the serial communication.
