Specialized Interfaces are special-purpose physical, electronic connections between devices that meet the requirements of adapting between particular bus standards. They tend to be optimized for that role – complying with special electronic characteristics and protocols needed to interface over a physical medium, connection method and networking architecture. This is achieved with a special device or devices that act as a bridge between subsystems or systems. Such devices have a local bus connection to enable the interface to the central processing units (CPUs) bus system. They also have one or more interfaces to the other physical medium (which could also be another local system bus connection).

 

An Interfaces primary role is to adapt between bus standards. They may also buffer data, flag events to the CPUs and even provide more complex functions like filtering. They can have the ability to send and receive data from the systems shared memory via direct memory access (DMA). Interface chips usually have a set of registers that hold configuration information programmed by a software driver running on the CPU. Sometimes specialized interface chips have to collate data to send (scatter-gather DMA) and the protocols they support functions such as error correction and signal equalization. They also have to have electrical driving characteristics compatible with the bus standards.

 

Specialized Interfaces tend to be serial or parallel. Short run very high bandwidth interfaces like computer motherboard memory buses are parallel. These can support extremely high transfer speeds, for example, GDDR5 chips as of 2015 can support 256Gbit/s transfer rates. These interfaces usually comply with low voltage differential standards, and have extremely tight guidelines for layout and can only be used over short distances, measured in inches.

 

Interfaces to peripheral cards or modules leave the main board, travel on rack back planes or between systems and are usually serial interfaces. These are single channels of I/O synchronized to a data clock that is either integrated with the data stream or a separate physical line. Interfaces such as PCIe are groups of serial interfaces called lanes and can provide a high-speed connection. For example, the Thunderbolt 2 protocol can support 20Gbit/s for up to 3m. These devices have special equalization and driving capabilities to allow very long cable runs (for example the latest video SDI serial interfaces support 12Gbit/S over 80metres of coaxial cable).

 

Many special purpose serial interfaces are lower bandwidth but are optimized for low cost and power consumption for minimum wired connections. These include asynchronous serial (UARTs) and synchronous serial (SPI, I2C) protocols. Other special purpose interfaces are optimized for wired or even wireless networking. Wired examples include Ethernet and RS485. Wireless examples include WIFI, Bluetooth, and Zigbee.