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2, 4 Meg x 64 SDRAM DIMMs
ZM02.p65 – Rev. 6/98
Micron Technology, Inc., reserves the right to change products or specifications without notice.
1998, Micron Technology, Inc.
3
2, 4 MEG x 64
SDRAM DIMMs
OBSOLETE
SPD CLOCK AND DATA CONV ENTIONS
Data states on the SDA line can change only during SCL
LOW. SDA state changes during SCL HIGH are reserved
for indicating start and stop conditions (Figures 1 and 2).
SPD START CONDITION
All commands are preceded by the start condition, which
is a HIGH-to-LOW transition of SDA when SCL is HIGH.
The SPD device continuously monitors the SDA and SCL
lines for the start condition and will not respond to any
command until this condition has been met.
SPD STOP CONDITION
All communications are terminated by a stop condition,
which is a LOW-to-HIGH transition of SDA when SCL is
HIGH. The stop condition is also used to place the SPD
device into standby power mode.
SPD ACKNOWLEDGE
Acknowledge is a software convention used to indicate
successful data transfers. The transmitting device, either
master or slave, will release the bus after transmitting eight
bits. During the ninth clock cycle, the receiver will pull the
SDA line LOW to acknowledge that it received the eight bits
of data (Figure 3).
The SPD device will always respond with an acknowl-
edge after recognition of a start condition and its slave
address. If both the device and a WRITE operation have
been selected, the SPD device will respond with an ac-
knowledge after the receipt of each subsequent eight-bit
word. In the read mode the SPD device will transmit eight
bits of data, release the SDA line and monitor the line for an
acknowledge. If an acknowledge is detected and no stop
condition is generated by the master, the slave will continue
to transmit data. If an acknowledge is not detected, the slave
will terminate further data transmissions and await the
stop condition to return to standby power mode.
SCL
SDA
DATA STABLE
DATA STABLE
DATA
CHANGE
Figure 1
DATA VALIDITY
SCL
SDA
START
BIT
STOP
BIT
Figure 2
DEFINITION OF START AND STOP
SCL from Master
Data Output
from Transmitter
Data Output
from Receiver
9
8
Acknowledge
Figure 3
ACKNOWLEDGE RESPONSE FROM RECEIVER