2.4 Serial EEPROM Interface

The LSI53C875A implements an interface that allows attachment of a serial EEPROM device to the GPIO0 and GPIO1 pins. There are two modes of operation relating to the serial EEPROM and the Subsystem ID and Subsystem Vendor ID registers. These modes are programmable through the MAD7 pin which is sampled at power-up.

2.4.1 Default Download Mode

In this mode, MAD7 is pulled down internally, GPIO0 is the serial data signal (SDA) and GPIO1 is the serial clock signal (SCL). Certain data in the serial EEPROM is automatically loaded into chip registers at power-up.

The format of the serial EEPROM data is defined in Table 2.7. If the download is enabled and an EEPROM is not present, or the checksum fails, the Subsystem ID and Subsystem Vendor ID registers read back all zeros. At power-up, only five bytes are loaded into the chip from locations 0xFB through 0xFF.

The Subsystem ID and Subsystem Vendor ID registers are read only, in accordance with the PCI specification, with a default value of all zeros if the download fails.

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Functional Description

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LSI 53C875A technical manual Serial Eeprom Interface, Default Download Mode