I/O Expander - Nokia RM-555 Service Manual

RM-555
System Module and User Interface
Figure 68 Bluetooth & FM radio block diagram

I/O Expander

I/O Expander is used for control signals that are not time critical, such as for keyboard inputs, enable & reset
signals etc. It is connected to the I2C bus, and has its own interrupt. PURX is used as I/O Expander's reset. I/
O Expander is powered from VIO 1.8V.
This device does not have a keyboard matrix, due to the minimal amount of keys needed in the touch input
concept. Instead, keys are connected as SF keys. This means that the keys connect each row to the ground.
Two control signals are controlled by the I/O Expander, TV-out reset signal and AVVideoCtrl. AVVideoCtrl is
used for two tasks: enabling TV out core regulator, and driving the switch that routes the TV out signal to
the signature connector.
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