View detail for Upgrading Two-Wire Serial EEPROM Memory

Upgrading Two-Wire Serial EEPROM Memory
1. Introduction
As applications are updated, many may require an increase in memory storage in
order to account for additional system data. This may require upgrading to a higher
density two-wire Serial EEPROM product. The below mentioned Atmel® two-wire
Serial EEPROM devices use the same package pin-out, and the same software protocol sequence making upgrading to a higher density product a simple and
straightforward process. However, there are a few differences to consider when
upgrading to a higher density.
• Memory page size
• Device / Word Address
2. Memory Page Size
The two-wire Serial EEPROM device family is divided into the following by memory
page size.
Device Part Number
Device Density
Page Size
AT24C01x/ C02x
1K, 2K(low density)
8 byte page
AT24C04x/ C08x/ C16x
4K, 8K, 16K (low density)
16 byte page
AT24C32x/ C64x
32K, 64K (medium density)
32 byte page
AT24C128x/ C256x
128K, 256K (high density)
64 byte page
AT24C512x/ AT24C1024x
512K, 1M (high density)
128 byte page
Upgrading
Two-Wire Serial
EEPROM
Memory
AT24C01x
AT24C02x
AT24C32x
AT24C64x
AT24C128x
AT24C256x
AT24C512x
AT24C1024x
All Atmel two-wire Serial EEPROM devices support both byte and page mode programming operations. As the page size increases, so does the ability to program more
data with a single write operation. For example it requires 4 separate sequential 8 byte
write sequences to program 32 consecutive bytes using a 2K device, but would only
require one 32 byte sequence to program those same locations using a 32K device.
This is a significant time savings considering each write cycle can take up to 5ms, thus
reducing programming time by a factor of four.
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3. Device / Word Address
3.1
Overview
Depending on density of device, Atmel two-wire serial communications requires a device
address followed by either one or two word address(s) for all write and read commands. The
device address will always starts with the two-wire identifier 1010 which establishes communication with the two-wire product family. Following the identifier are the device / page address bits.
For the low density family (1K – 16K) only one word address follows the device address. Since
an eight bit address field can only access 256 different byte locations (2K bits), the 4K-16K
devices make use of page address bits embedded in the device address field. These page
address bits are traded off with the Device / Page address pins 1, 2, and 3 thus resulting in the
reduced cascadability. The medium and high density device use a two word address therefore,
devices 32K – 512K all have 8 device cascadability with only the 1 Meg device needing to use
the a single embedded page address bit. The below table (refer to Figure 3-1) is provided for
easy reference to determine these device / word address differences and bus cascadability.
Figure 3-1.
Two-Wire Family Attributes
Device Address / Page Byte
3.2
Word Address Bytes
Maximum Devices on Bus
1K/2K
1
0
1
0
A2
A1
A0 R/W
1
8
4K
1
0
1
0
A2
A1
P0 R/W
1
4
8K
1
0
1
0
A2
P1
P0 R/W
1
2
16K
1
0
1
0
P2
P1
P0 R/W
1
1
32K-512K
1
0
1
0
A2
A1
A0 R/W
2
8
1M
1
MSB
0
1
0
A2
A1
P0 R/W
LSB
2
4
Upgrades within the Low Density Family
The low density family (1K – 16K) all use a single word address (refer to Figure 3-2). When
upgrading within the low density family the difference in device / page pin configuration needs to
be considered along with differences in page size. All other features and commands are the
same.
2
AT24C01B/C02B/C04B/C08B/C16B/C32C/C64C/C128B/C256B/C512B/C1024B
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AT24C01B/C02B/C04B/C08B/C16B/C32C/C64C/C128B/C256B/C512B/C1024B
3.3
Upgrades from Low Density to Medium and High Densities
Upgrading from low to medium and high density will require the additional byte of word address
(refer to Figure 3-3). Therefore system software will need to be adjusted to compensate for the
extra word address. Also any differences in the device / page address bits will need to be considered along with changes in page size.
3.4
Upgrades within and from Medium to High Densities
All devices from 32K – 512K will require no system changes and can be interchanged with only
the page size differences to consider.
Figure 3-2.
Low Density Random Read
S
T
A
R
T
W
R
I
T
E
DEVICE
ADDRESS
S
T
A
R
T
WORD
ADDRESS n
S
T
O
P
R
E
A
D
DEVICE
ADDRESS
*
SDA LINE
M
S
B
L R A
S / C
BW K
M
S
B
L A
S C
B K
M
S
B
L
S
B
DATA n
A
C
K
A
C
K
DUMMY WRITE
Figure 3-3.
N
O
Medium and High Density Random Read
S
T
A
R
T
DEVICE
ADDRESS
W
R
I
T
E
S
T
A
R
T
1st, 2nd WORD
ADDRESS n
DEVICE
ADDRESS
S
T
O
P
R
E
A
D
0
SDA LINE
M
S
B
L R A
S / C
BW K
M
S
B
DUMMY WRITE
L A
S C
B K
A
C
K
DATA n
N
O
A
C
K
4. Conclusion
Upgrading density within the two wire family is a straightforward process as long as you consider
the following possible differences.
• Page sizes changes
• Device / Page address configuration
• One or Two word address byte(s)
3
5237A–SEEPR–4/07
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