Legacy-Free Keyboard/Embedded Controller with SPI and LPC Docking Interface
Chapter 15 I2C/SMBus
15.1
Overview
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The LPC47N350 supports I C/SMBus. I C/SMBus is a serial communication protocol between a
computer host and its peripheral devices. It provides a simple, uniform and inexpensive way to connect
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peripheral devices to a single computer port. A single I C/SMBus controller on a host can accommodate
up to 125 peripheral devices.
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The I C/SMBus protocol includes a physical layer and several software layers. The software layers
include the base protocol, the device driver interface, and several specific device protocols.
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The LPC47N350 implements two I C/SMBus controllers (I C/SMBus 1 Controller and I C/SMBus 2
Controller). Each controller, through a multiplexer, can drive two independent sets of Clock and Data
pins, as shown in Figure 15.1, "I2C/SMBus Controllers".
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Four I C/SMBus 2 controller pins, AB2A_DATA, AB2A_CLK, AB2B_DATA and AB2B_CLK are
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multiplexed on GPIO11 through GPIO14. For information regarding multiplexed I C/SMBus pins see
Table 2.4 on page 10 and Section 21.5, "Multiplexing_3 Register - MISC[23:17]".
APPLICATION NOTE: When VCC1=0, the I2C bus pins present a high impedance and draw only leakage current.
Therefore no additional external circuity is required to isolate the LPC47N350 Vcc1 powered
the I2C bus pins from an I2C bus with VCC0 powered devices and/or resistor pull-ups to
VCC0.
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The I C/SMBus interface is fully and directly controlled by the on-chip 8051 through its set of on-chip
memory mapped control registers. Addresses for the registers are shown in Table 15.1, "I2C/SMBus
Register Address Summary".
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The I C/SMBus logic is powered on the VCC1 power plane and clocked by the 8051 clock to provide
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the ability to wake-up the 8051 on an I C/SMBus event. When a wakeup event occurs, there is a 6 µs
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max. delay before the ring oscillator starts and an I C/SMBus event can be detected. This limits the
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I C/SMBus Bus Master Operating Frequency for wakeup events to 60 KHz. Once the ring oscillator is
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running, the I C/SMBus Operating Frequency is a full 100 KHz.
SMSC LPC47N350
165
Revision 1.1 (01-14-03)
DATASHEET
SMSC [ SMSC CORPORATION ]
