X4045 INTERSIL [Intersil Corporation], X4045 Datasheet - Page 13

• Manufacturer Part Number: X4045
• Description: CPU Supervisor with 4kbit EEPROM
• Manufacturer: INTERSIL [Intersil Corporation]

Acknowledge Polling
The disabling of the inputs during nonvolatile cycles
can be used to take advantage of the typical 5kHz
write cycle time. Once the stop condition is issued to
indicate the end of the master’s byte load operation,
the device initiates the internal nonvolatile cycle.
Acknowledge polling can be initiated immediately. To
do this, the master issues a start condition followed by
the slave address byte for a write or read operation. If
the device is still busy with the nonvolatile cycle then
no ACK will be returned. If the device has completed
the write operation, an ACK will be returned and the
host can then proceed with the read or write operation.
Refer to the flow chart in Figure 13.
Serial Read Operations
Read operations are initiated in the same manner as
write operations with the exception that the R/W bit of
the slave address byte is set to one. There are three
basic read operations: Current Address Reads, Ran-
dom Reads, and Sequential Reads.
Current Address Read
Internally the device contains an address counter that
maintains the address of the last word read incre-
mented by one. Therefore, if the last read was to
address n, the next read operation would access data
from address n+1. On power-up, the address of the
address counter is undefined, requiring a read or write
operation for initialization.
Upon receipt of the slave address byte with the R/W bit
set to one, the device issues an acknowledge and then
transmits the eight bits of the data byte. The master ter-
minates the read operation when it does not respond
with an acknowledge during the ninth clock and then
issues a stop condition. Refer to Figure 13 for the
address, acknowledge, and data transfer sequence.
Figure 14. Current Address Read Sequence
13
Signals from
Signals from
the Master
the Slave
SDA Bus
S
a
t
r
t
X4043, X4045
Address
Slave
1
Figure 13. Acknowledge Polling Sequence
It should be noted that the ninth clock cycle of the read
operation is not a “don’t care.” To terminate a read
operation, the master must either issue a stop condi-
tion during the ninth cycle or hold SDA HIGH during
the ninth clock cycle and then issue a stop condition.
A
C
K
Continue Normal Read
Data
Byte Load Completed
Issue Slave Address
Byte (Read or Write)
Complete. Continue
or Write Command
Enter ACK Polling
by Issuing STOP.
Nonvolatile Cycle
Issue START
PROCEED
Sequence
Returned?
Command
ACK
S
o
p
YES
YES
t
NO
NO
Issue STOP
Issue STOP
March 16, 2006
FN8118.2