FM24C04A_05 RAMTRON [Ramtron International Corporation], FM24C04A_05 Datasheet - Page 6

• Manufacturer Part Number: FM24C04A_05
• Description: 4Kb FRAM Serial Memory
• Manufacturer: RAMTRON [Ramtron International Corporation]

Read Operation
There are two basic types of read operations. They are
current address read and selective address read. For
current address reads, the FM24C04A 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.
Current Address & Sequential Read
The FM24C04A 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.
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 FM24C04A 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.
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
FM24C04A 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 FM24C04A
Rev. 3.0
Mar. 2005
By FM24C04A
By Master
By FM24C04A
By Master
a
Start
S
byte,
Start
S
Slave Address
this
Slave Address
indicates
0
A
Figure 6. Multiple Byte Write
that
Figure 5. Byte Write
0
Address & Data
Word Address
A
the
Address & Data
Word Address
attempts to read out additional data onto the bus. The
four valid methods are as follows.
1.
2.
3.
4.
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 and
sequential reads.
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 FM24C04A 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.
A
The bus master issues a no-acknowledge in the
9
This is illustrated in the diagrams below. This is
the preferred method.
The bus master issues a no-acknowledge in the
9
The bus master issues a stop in the 9
cycle. Bus contention may result.
The bus master issues a start in the 9
cycle. Bus contention may result.
th
th
clock cycle and a stop in the 10
clock cycle and a start in the 10
Acknowledge
Acknowledge
Data Byte
A
Data Byte
A
Data Byte
th
th
A
.
clock cycle.
Stop
FM24C04A
P
th
th
A
Stop
clock
clock
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P