Serial Interface Description
MASTER:
The device that generates the serial clock.
SLAVE:
Because the Serial Clock pin (SCK) is always an
input, the AT25010/020/040 always operates as a slave.
TRANSMITTER/RECEIVER:
The AT25010/020/040 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.
The op-code also contains address bit A8 in both the
READ and WRITE instructions.
INVALID OP-CODE:
If an invalid op-code is received, no
data will be shifted into the AT25010/020/040, 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 AT25010/020/040 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 AT25010/020/040. 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, all write operations are inhibited.
WP going low while CS is still low will interrupt a write to the
AT25010/020/040. If the internal write cycle has already
been initiated, WP going low will have no effect on any
write operation.
SPI Serial Interface
6
AT25010/020/040
ATMEL [ ATMEL CORPORATION ]
