LAN9220 datasheet(30/142 Pages) MICROCHIP

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LAN9220

DS00002417A-page 30

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3.9

EEPROM Interface

The LAN9220 can optionally load its MAC address from an external serial EEPROM. If a properly configured EEPROM

is detected by the LAN9220 at power-up, hard reset or soft reset, the ADDRH and ADDRL registers will be loaded with

the contents of the EEPROM. If a properly configured EEPROM is not detected, it is the responsibility of the host LAN

Driver to set the IEEE addresses.

The LAN9220 EEPROM controller also allows the host system to read, write and erase the contents of the Serial

EEPROM. The EEPROM controller supports most “93C46” type EEPROMs configured for 128 x 8-bit operation.

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, "ADDRL—MAC Address Low Register," on page 96.

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 suc-

cessful 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, "E2P_CMD – EEPROM Command Register," on page 89 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

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

pletion 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 com-

mand 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 register.

If an operation is attempted, and an EEPROM device does not respond within 30mS, the LAN9220 will timeout, and the

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

Figure 3-10, "EEPROM Access Flow Diagram" illustrates the host accesses required to perform an EEPROM Read or

Write operation.

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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