LAN89218 datasheet(34/148 Pages) MICROCHIP

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LAN89218

DS60001255B-page 34

 2008-2015 Microchip Technology Inc.

3.9.1

MAC ADDRESS AUTO-LOAD

On power-up, hard reset or soft reset, the EEPROM controller attempts to read the first byte of data from the

EEPROM (address 00h). If the value A5h is read from the first address, then the EEPROM controller will assume

that an external Serial EEPROM is present. The EEPROM controller will then access the next EEPROM byte and

send it to the MAC Address register byte 0 (ADDRL[7:0]). This process will be repeated for the next five bytes of the

MAC Address, thus fully programming the 48-bit MAC address. Once all six bytes have been programmed, the “MAC

Address Loaded” bit is set in the E2P_CMD register. A detailed explanation of the EEPROM byte ordering with

respect to the MAC address is given in Section 5.4.3.

If an 0xA5h is not read from the first address, the EEPROM controller will end initialization. It is then the responsibility

of the host LAN driver software to set the IEEE address by writing to the MAC’s ADDRH and ADDRL registers.

The host can initiate a reload of the MAC address from the EEPROM by issuing the RELOAD command via the E2P

command (E2P_CMD) register. If the first byte read from the EEPROM is not A5h, it is assumed that the EEPROM

is not present, or not programmed, and the MAC address reload will fail. The “MAC Address Loaded” bit indicates

a successful reload of the MAC address.

3.9.2

EEPROM HOST OPERATIONS

After the EEPROM controller has finished reading (or attempting to read) the MAC after power-on, hard reset or soft

reset, the host is free to perform other EEPROM operations. EEPROM operations are performed using the E2P_CMD

and E2P data (E2P_DATA) registers. Section 5.3.23 provides an explanation of the supported EEPROM operations.

If the EEPROM operation is the “write location” (WRITE) or “write all” (WRAL) commands, the host must first write

the desired data into the E2P_DATA register. The host must then issue the WRITE or WRAL command using the

E2P_CMD register by setting the EPC_CMD field appropriately. If the operation is a WRITE, the EPC_ADDR field in

E2P_CMD must also be set to the desired location. The command is executed when the host sets the EPC_BSY bit

high. The completion of the operation is indicated when the EPC_BSY bit is cleared.

If the EEPROM operation is the “read location” (READ) operation, the host must issue the READ command using

the E2P_CMD with the EPC_ADDR set to the desired location. The command is executed when the host sets the

EPC_BSY bit high. The completion of the operation is indicated when the EPC_BSY bit is cleared, at which time the

data from the EEPROM may be read from the E2P_DATA register.

Other EEPROM operations are performed by writing the appropriate command to the EPC_CMD register. The

command is executed when the host sets the EPC_BSY bit high. The completion of the operation is indicated when

the EPC_BSY bit is cleared. In all cases the host must wait for EPC_BSY to clear before modifying the E2P_CMD

If an operation is attempted, and an EEPROM device does not respond within 30 ms, the LAN89218 will timeout,

and the EPC timeout bit (EPC_TO) in the E2P_CMD register will be set.

Note:

The EEPROM device powers-up in the erase/write disabled state. To modify the contents of the EEPROM

the host must first issue the EWEN command.

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