Rainbow Electronics AT25040A - Manual (Page 5)

5
AT25010A/020A/040A [Preliminary]
3402A–SEEPR–10/3/03
Serial Interface
Description
MASTER: The device that generates the serial clock.
S L A V E : B e c a u s e t h e S e r i a l C l o c k p i n ( S C K ) i s a l w a y s a n i n p u t , t h e
AT25010A/020A/040A always operates as a slave.
TRANSMITTER/RECEIVER: The AT25010A/020A/040A 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
AT25010A/020A/040A, 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 AT25010A/020A/040A 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.
H O L D : T h e H O LD p i n i s u se d i n co n j un cti o n w it h the C S pi n to s e le ct th e
AT25010A/020A/040A. 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 AT25010A/020A/040A. If
the internal write cycle has already been initiated, WP going low will have no effect on
any write operation.