Interface refers to matching between a sender and a receiver, with respect to connection. When a human being intends to transmit his or her thoughts verbally, for example, the words will not be able to be understood unless the person speaks loud enough and the other party intends to hear the words. Incidentally, "man-machine interface" means that a system supplies a display, voice, and/or operability that a human being can understand.
When two semiconductor devices are to be connected, the voltage and timing of the change of signaling of the two must be matched. For signaling, in addition to that of the TTL (Transistor-Transistor Logic) and CMOS levels (refer to Tea Breakunder Pull-up/pull-down ), the following high-speed interfaces using low-voltage signals or signal differentials are available.
|Interface||Voltage||Termination||Standard||Speed example||Application example|
(Low Voltage TTL/ Low Voltage CMOS)
|HSTL Class I |
(High-Speed Transceiver Logic)
|HSTL Class II||1.5V||JEDEC |
|Differential HSTL||1.5V||JEDEC |
|SSTL-3 Class I, II |
(Stub Series Terminated Logic)
|SSTL-2 Class I, II||2.5V||JEDEC |
|160-400MHz||DDR I SDRAM|
|Differential SSTL-2||2.5V||160-400MHz||DDR I SDRAM|
(Gunning Transceiver Logic)
(Low Voltage Differential Signaling)
(Low Voltage Positive Emitter Coupled Logic)
(Peripheral Component Interconnect bus)
|AGP 1x, 2x |
(Accelerated Graphics Port)
When two systems are connected, matching of communication procedures (protocols) such as identification, sequencing, and checking is also necessary. Interfaces are divided into two types: serial and parallel. While a serial interface transfers data 1 bit at a time, making a waiting queue long, a parallel interface can transfer data of two or more bits at the same time. For example, a 133 MHz 64-bit parallel PCI has a bandwidth of up to 8.5 Gbps (133 M x 64). ISDN, which is a 128 kbps serial interface, is called a broad band system, but parallel interfaces can transfer an overwhelming quantity of data per unit time. Parallel interfaces, however, require two or more signal lines, and synchronizing these lines is a problem that must be solved.