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The PCA9558 is a highly integrated, multi-function device that is composed of a 5-bit
multiplexed/1-bit latched 6-bit I²C-bus/SMBus EEPROM DIP switch, an 8-bit I/O expander
and a 2-kbit serial EEPROM with write protect. The PCA9558 integrates these commonly
used components into a single chip to reduce component count and board space
requirements and is useful in computer, server and telecom/networking applications.
Multiplexed/latched EEPROM DIP switch — used to select digital information
between a set of 5 bits of default hardware inputs and an alternative set of inputs
provided by the I²C-bus/SMBus interface and stored in the EEPROM. Examples of
this type of selection include processor voltage configuration or processor vendor
identification (VID). The multiplexed/latched EEPROM can also be used to replace
DIP switches or jumpers since the settings can be easily changed via I²C-bus/SMBus
without having to power down the equipment to open the cabinet. The non-volatile
memory retains the most current setting selected before the power is turned off.
8-bit I/O expander — used to control, monitor or collect remote information or power
LEDs. Monitored or collected information can be read through the I²C-bus/SMBus or
can be stored in the internal EEPROM.
2-kbit serial EEPROM — used to store information such as card identification or
revision/maintenance history on every motherboard/line card and can be read or
written via I²C-bus/SMBus when required.
The PCA9558 has one address pin, allowing up to two devices to be placed on the same
I²C-bus or SMBus.