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PC components and systems which involve I 2 C are serial presence detect (SPD) EEPROMs on dual in-line memory modules (DIMMs), Extended Display Identification Data (EDID) for monitors via VGA, DVI and HDMI connectors, accessing NVRAM chips, etc. Common I2C applications include reading hardware monitors, sensors, real-time clocks, controlling ...
Data bits output on blue lines if CPHA=0, or on red lines if CPHA=1, and sample on opposite-colored lines. Numbers identify data bits. Z indicates high impedance. The SPI timing diagram shown is further described below: CPOL represents the polarity of the clock. Polarities can be converted with a simple inverter.
The figures below are simplex data rates, which may conflict with the duplex rates vendors sometimes use in promotional materials. Where two values are listed, the first value is the downstream rate and the second value is the upstream rate. The use of decimal prefixes is standard in data communications.
The communication links, across which computers (or parts of computers) talk to one another, may be either serial or parallel. A parallel link transmits several streams of data simultaneously along multiple channels (e.g., wires, printed circuit tracks, or optical fibers); whereas, a serial link transmits only a single stream of data.
The HDR-DDR mode uses double data rate signalling on the SDA line with a 12.5 MHz clock to achieve a 25 Mbit/s raw data rate (20 Mbit/s effective). This requires changing the SDA line while SCK is high, a violation of the I²C protocol, but as the high-going pulse is only 40 ns long, I²C devices will ignore it and thus not notice the violation.
English: A sequence diagram of data transfer on the I²C bus S - Start condition; P - Stop condition; B - transferring of one bit; SDA changes are allowed when SCL is low (blue), otherwise there will be a start or stop condition generated
Asynchronous start-stop is the lower data-link layer used to connect computers to modems for many dial-up Internet access applications, using a second (encapsulating) data link framing protocol such as PPP to create packets made up out of asynchronous serial characters. The most common physical layer interface used is RS-232D.
Before a register access, PHY devices generally require a preamble of 32 ones to be sent by the MAC on the MDIO line. The access consists of 16 control bits, followed by 16 data bits. The control bits consist of 2 start bits, 2 access type bits (read or write), the PHY address (5 bits), the register address (5 bits), and 2 "turnaround" bits.