FM24CL04B
Start
S
Address & Data
Word Address
Stop
By Master
Slave Address
0
A
A
Data Byte
A
P
By FM24CL04B
Acknowledge
Figure 5. Byte Write
Start
Address & Data
Word Address
Stop
By Master
S
Slave Address
0
A
A
Data Byte
A
Data Byte
A
P
By FM24CL04B
Acknowledge
Figure 6. Multiple Byte Write
attempts to read out additional data onto the bus. The
four valid methods are as follows.
Read Operation
There are two basic types of read operations. They are
current address read and selective address read. In a
current address read, the FM24CL04B uses the
internal address latch to supply the lower 8 address
bits. In a selective read, the user performs a procedure
to set these lower address bits to a specific value.
1. The bus master issues a no-acknowledge in the
9th clock cycle and a stop in the 10th clock cycle.
This is illustrated in the diagrams below. This is
the preferred method.
2. The bus master issues a no-acknowledge in the
9th clock cycle and a start in the 10th.
3. The bus master issues a stop in the 9th clock
cycle. Bus contention may result.
Current Address & Sequential Read
The FM24CL04B uses an internal latch to supply the
lower 8 address bits for a read operation. A current
address read uses the existing value in the address
latch as a starting place for the read operation. This is
the address immediately following that of the last
operation.
4. The bus master issues a start in the 9th clock
cycle. Bus contention may result.
If the internal address reaches 1FFh it will wrap
around to 000h on the next read cycle. Figures 7 and
8 show the proper operation for current address reads.
To perform a current address read, the bus master
supplies a slave address with the LSB set to 1. This
indicates that a read operation is requested. The page
select bit in the slave address specifies the block of
memory that is used for the read operation. After the
acknowledge, the FM24CL04B will begin shifting out
data from the current address. The current address is
the bit from the slave address combined with the 8 bits
that were in the internal address latch.
Selective (Random) Read
A simple technique allows a user to select a random
address location as the starting point for a read
operation. This involves using the first two bytes of a
write operation to set the internal address byte
followed by subsequent read operations.
To perform a selective read, the bus master sends out
the slave address with the LSB set to 0. This specifies
a write operation. According to the write protocol, the
bus master then sends the word address byte that is
loaded into the internal address latch. After the
FM24CL04B acknowledges the word address, the bus
master issues a start condition. This simultaneously
aborts the write operation and allows the read
command to be issued with the slave address LSB set
to a 1. The operation is now a current address read.
See Figure 9.
Beginning with the current address, the bus master can
read any number of bytes. Thus a sequential read is
simply a current address read with multiple byte
transfers. After each byte the internal address counter
will be incremented. Each time the bus master
acknowledges
a
byte, this indicates that the
FM24CL04B should read out the next sequential byte.
There are four ways to properly terminate a read
operation. Failing to properly terminate the read will
most likely create a bus contention as the FM24CL04B
Rev. 1.3
Feb. 2011
Page 6 of 12
RAMTRON [ RAMTRON INTERNATIONAL CORPORATION ]
