X1243 – Preliminary Information
Figure 5. Acknowledge Response From Receiver
SCL from
Master
1
8
9
Data Output
from Transmitter
Data Output
from Receiver
Start
Acknowledge
Acknowledge
WRITE OPERATIONS
Byte Write
Acknowledge is a software convention used to indicate
successful data transfer. 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. Refer to Figure 5.
For a byte write operation (Refer to Figure 13), the
device requires the Slave Address Byte and the Word
Address Bytes. This gives the master access to any
one of the words in the array or CCR. (Note: Prior to
writing to the CCR, the master must write a 02h, then
06h to the status register in preceding operations to
enable the write operation. See “Writing to the Clock/
Control Registers” on page 6.) Upon receipt of each
address byte, the X1243 responds with an acknowl-
edge. After receiving both address bytes the X1243
awaits the eight bits of data. After receiving the 8 data
bits, the X1243 again responds with an acknowledge.
The master then terminates the transfer by generating
a stop condition. The X1243 then begins an internal
write cycle of the data to the nonvolatile memory. Dur-
ing the internal write cycle, the device inputs are dis-
abled, so the device will not respond to any requests
from the master. The SDA output is at high impedance.
See Figure 6.
The device will respond with an acknowledge after rec-
ognition of a start condition and if the correct Device
Identifier and Select bits are contained in the Slave
Address Byte. If a write operation is selected, the
device will respond with an acknowledge after the
receipt of each subsequent eight bit word. The device
will acknowledge all incoming data and address bytes,
except for:
– The Slave Address Byte when the Device Identifier
and/or Select bits are incorrect
– All Data Bytes of a write when the WEL in the Write
Protect Register is LOW
– The 2nd Data Byte of a Register Write Operation
(when only 1 data byte is allowed)
A write to a protected block of memory is ignored, but
will still receive an acknowledge. At the end of the write
command, the X1243 will not initiate an internal write
cycle, and will continue to ACK commands.
In the read mode, the device will transmit eight bits of
data, release the SDA line, then monitor the line for an
acknowledge. If an acknowledge is detected and no
stop condition is generated by the master, the device
will continue to transmit data. The device will terminate
further data transmissions if an acknowledge is not
detected. The master must then issue a stop condition
to return the device to Standby mode and place the
device into a known state.
Characteristics subject to change without notice. 8 of 18
REV 1.1.4 5/31/01
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