SMSC LAN9500 - Manual (Page 20)

Hi-Speed USB 2.0 to 10/100 Ethernet Controller
Datasheet
Revision 1.7 (10-02-08) 20 SMSC LAN9500/LAN9500i
DATASHEET
Chapter 3 EEPROM Controller (EPC)
LAN9500/LAN9500i may use an external EEPROM to store the default values for the USB descriptors
and the MAC address. The EEPROM controller supports most “93C46” type EEPROMs. The
EEP_SIZE strap selects the size of the EEPROM attached to LAN9500/LAN9500i. When this strap is
set to “0”, a 128 byte EEPROM is attached and a total of seven address bits are used. When this strap
is set to “1” a 256/512 byte EEPROM is attached and a total of nine address bits are used.
Note: A 3-wire style 1K/2K/4K EEPROM that is organized for 128 x 8-bit or 256/512 x 8-bit operation
must be used.
The MAC address is used as the default Ethernet MAC address and is loaded into the MAC’s ADDRH
and ADDRL registers. If a properly configured EEPROM is not detected, it is the responsibility of the
Host LAN Driver to set the IEEE addresses.
After a system-level reset occurs, LAN9500/LAN9500i will load the default values from a properly
configured EEPROM. LAN9500/LAN9500i will not accept USB transactions from the Host until this
process is completed.
The LAN9500/LAN9500i EEPROM controller also allows the Host system to read, write and erase the
contents of the Serial EEPROM.
3.1 EEPROM Format
Table 3.1 illustrates the format in which data is stored inside of the EEPROM.
Note the EEPROM offsets are given in units of 16-bit word offsets. A length field with a value of zero
indicates that the field does not exist in the EEPROM. The LAN9500/LAN9500i will use the field’s HW
default value in this case.
Note: For the device descriptor, the only valid values for the length are 0 and 18.
Note: For the configuration and interface descriptor, the only valid values for the length are 0 and 18.
Note: The EEPROM programmer must ensure that if a string descriptor does not exist in the
EEPROM, the referencing descriptor must contain 00h for the respective string index field.
Note: If all string descriptor lengths are zero, then a Language ID will not be supported.
Table 3.1 EEPROM Format
EEPROM ADDRESS EEPROM CONTENTS
00h 0xA5
01h MAC Address [7:0]
02h MAC Address [15:8]
03h MAC Address [23:16]
04h MAC Address [31:24]
05h MAC Address [39:32]
06h MAC Address [47:40]
07h Full-Speed Polling Interval for Interrupt Endpoint
08h Hi-Speed Polling Interval for Interrupt Endpoint