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Data transfer is initiated with a start condition (S) signalled by SDA being pulled low while SCL stays high. SCL is pulled low, and SDA sets the first data bit level while keeping SCL low (during blue bar time). The data is sampled (received) when SCL rises for the first bit (B1).
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 first data bit is output immediately when SS activates. Subsequent bits are output when SCLK transitions to its idle voltage level. Sampling occurs when SCLK transitions from its idle voltage level. For CPHA=1: The first data bit is output on SCLK's first clock edge after SS activates.
Between data frames, the bus controller holds SCL high, in effect stopping the clock, and SDA drivers are in a high-impedance state, permitting a pull-up resistor to float it to high. A high-to-low transition of SDA while SCL is high is known as a START symbol, and signals the beginning a new data frame.
It carries clock, data, and instructions and is based on Philips' I²C serial bus protocol. [1] Its clock frequency range is 10 kHz to 100 kHz. (PMBus extends this to 400 kHz.) Its voltage levels and timings are more strictly defined than those of I²C, but devices belonging to the two systems are often successfully mixed on the same bus.
The Hi-Z state's purpose is to effectively remove a device's influence from the rest of the circuit. If multiple devices output to a shared wire, no device should drive the shared wire to one logical voltage level when another device drives the shared wire to another logical voltage level, since that competition would result in excessive current draw through the short circuit and an uncertain ...
Current mode logic (CML), or source-coupled logic (SCL), is a digital design style used both for logic gates and for board-level digital signaling of digital data.. The basic principle of CML is that current from a constant current generator is steered between two alternate paths depending on whether a logic zero or logic one is being represented.
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.