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Serial Bus Analysis
R&S
®
RTB2000
180User Manual 1333.1611.02 ─ 03
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The I²C Protocol....................................................................................................180
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I
2
C Configuration...................................................................................................182
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I
2
C Trigger.............................................................................................................183
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I
2
C Decode Results ..............................................................................................186
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I
2
C Label List.........................................................................................................187
12.3.1 The I²C Protocol
This chapter provides an overview of protocol characteristics, data format, address
types and trigger possibilities. For detailed information, read the "I2C-bus specification
and user manual" available on the NXP manuals web page at
http://www.nxp.com/.
I²C characteristics
Main characteristics of I²C are:
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Two-wire design: serial clock (SCL) and serial data (SDA) lines
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Master-slave communication: the master generates the clock and addresses the
slaves. Slaves receive the address and the clock. Both master and slaves can
transmit and receive data.
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Addressing scheme: each slave device is addressable by a unique address. Multi-
ple slave devices can be linked together and can be addressed by the same mas-
ter.
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Read/write bit: specifies if the master will read (=1) or write (=0) the data.
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Acknowledge: takes place after every byte. The receiver of the address or data
sends the acknowledge bit to the transmitter.
The R&S RTB2000 supports all operating speed modes: high-speed, fast mode plus,
fast mode, and standard mode.
Data transfer
The format of a simple I²C message (frame) with 7 bit addressing consists of the fol-
lowing parts:
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Start condition: a falling slope on SDA while SCL is high
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7-bit address of the slave device that either will be written to or read from
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R/W bit: specifies if the data will be written to or read from the slave
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ACKnowledge bits: is issued by the receiver of the previous byte if the transfer was
successful
Exception: At read access, the master terminates the data transmission with a
NACK bit after the last byte.
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Data: a number of data bytes with an ACK bit after every byte
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Stop condition: a rising slope on SDA while SCL is high
I²C (Option R&S RTB-K1)
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