Fusion 878A
3.0 Electrical Interfaces
PCI Video Decoder
3.5 I2C Serial EEPROM Interface
100600B
Conexant
3-23
3.5 I
2
C Serial EEPROM Interface
The external EEPROM must reside on the I
2
C bus (SDA, SCL). This interface
supports the IC’s equivalent to the 24C02 or 24C02A 2 k bit 5 V CMOS Serial
EEPROM. The 7-bit slave device address is 1010000. The EEPROM can be read
anytime using the I
2
C hardware or software modes. The read transaction
sequence is:
1.
START
2.
0xA0
3.
8-bit byte address
4.
START
5.
0xA1
6.
8-bit read data, followed by (master NACK &) STOP
Thus, a normal 2-byte write transaction without STOP followed by a 2-byte
read transaction allows random access to a data byte.
3.5.1 EEPROM Address Mapping
Fusion 878A can support one EEPROM (max 256 B), typically a single 24C02.
Re-map the 8-bit addressable physical memory space to an 8-bit logical address
space by inverting the address A[7:0], and subtracting 4. The 7-bit slave device
address is 1010_xxx where the xxx bits are (normally used for A[10:8]) set to
zero. The A2, A1, A0 pins on the 24C02 device should be tied low to match.
Re-mapping the address space in this way allows the subsystem IDs to be
stored at a fixed physical base address and have the read-only section precede the
read-writable section. The entire address range (rather than some sub-portion) is
inverted to maintain physical address continuity. The address translation applies
only when the hardware accesses subsystem IDs or vital product data. If SW uses
the I
2
C function to directly address the EEPROM, the actual physical address
must be used.
Table 3-6. External EEPROM Memory Map
Logical Address
Physical Address
24C02
251
0x00
Read/Write
...
...
124
0x7F
123
0x80
Read-Only
...
...
–4
0xFF