FM24C04 Просмотр технического описания (PDF) - Fairchild Semiconductor
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FM24C04 Datasheet PDF : 14 Pages
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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 is set to a one. There are three basic read operations:
current address read, random read, and sequential read.
Current Address Read
Internally the FM24C04U/05U contains an address counter that
maintains the address of the last byte accessed, incremented by
one. Therefore, if the last access (either a read or write) was to
address n, the next read operation would access data from
address n + 1. Upon receipt of the slave address with R/W set to
one, the FM24C04U/05U issues an acknowledge and transmits
the eight bit word. The master will not acknowledge the transfer
but does generate a stop condition, and therefore the FM24C04U/
05U discontinues transmission. Refer to Figure 6 for the se-
quence of address, acknowledge and data transfer.
Random Read
Random read operations allow the master to access any memory
location in a random manner. Prior to issuing the slave address
with the R/W bit set to one, the master must first perform a
“dummy” write operation. The master issues the start condition,
slave address with the R/W bit set to zero and then the byte
address is read. After the byte address acknowledge, the master
immediately issues another start condition and the slave address
with the R/W bit set to one. This will be followed by an acknowl-
edge from the FM24C04U/05U and then by the eight bit word. The
master will not acknowledge the transfer but does generate the
stop condition, and therefore the FM24C04U/05U discontinues
transmission. Refer to Figure 7 for the address, acknowledge, and
data transfer sequence.
Sequential Read
Sequential reads can be initiated as either a current address read
or random access read. The first word is transmitted in the same
manner as the other read modes; however, the master now
responds with an acknowledge, indicating it requires additional
data. The FM24C04U/05U continues to output data for each
acknowledge received. The read operation is terminated by the
master not responding with an acknowledge or by generating a
stop condition.
The data output is sequential with the data from address n
followed by the data from n + 1. The address counter for read
operations increments all word address bits, allowing the entire
memory contents to be serially read during one operation. After
the entire memory has been read, the counter "rolls over" to the
beginning of the memory. FM24C04U/05U continues to output
data for each acknowledge received. Refer to Figure 8 for the
address, acknowledge, and data transfer sequence.
Current Address Read (Figure 6)
S
T
Bus Activity:
A
Master
R
T
SLAVE
ADDRESS
SDA Line
101 0
1
A
Bus Activity:
C
EEPROM
K
S
T
O
P
NO
DATA
A
C
K
Random Read (Figure 7)
S
T
Bus Activity: A
Master
R
T
SLAVE
ADDRESS
WORD
ADDRESS
S
T
A
SLAVE
R
ADDRESS
T
SDA Line
Bus Activity:
EEPROM
A
A
A
C
C
C
K
K
K
S
T
O
P
NO
DATA n
A
C
K
Sequential Read (Figure 8)
Bus Activity:
Master
Slave
Address
SDA Line
Bus Activity:
EEPROM
A
C
DATA n +1
K
A
A
A
C
C
C
K
K
K
DATA n +1
DATA n + 2
S
T
O
P
NO
DATA n + x
A
C
K
12
FM24C04U/05U Rev. A.3
www.fairchildsemi.com
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