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What is Interface?

Latest Updated:10/01/2006

Question:

What is Interface?

Answer:

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
LVTTL/LVCMOS
(Low Voltage TTL/
Low Voltage CMOS)
3.3V   JEDEC
JESD8-B
350MHz  
2.5V   JEDEC
JESD8-5
350MHz  
1.8V   JEDEC
JESD8-7
250MHz  
LVCMOS 1.5V   JEDEC
JESD8-11
225MHz  
HSTL Class I
(High-Speed Transceiver
Logic)
1.5V JEDEC
JESD8-6
150-225MHz QDRSRAM
HSTL Class II 1.5V JEDEC
JESD8-6
150-250MHz QDRSRAM
Differential HSTL 1.5V JEDEC
JESD8-6
150-225MHz CLK interface
SSTL-3 Class I, II
(Stub Series Terminated
Logic)
3.3V JEDEC
JESD8-8
167MHz SDRAM
SSTL-2 Class I, II 2.5V JEDEC
JESD8-9A
160-400MHz DDR I SDRAM
Differential SSTL-2 2.5V   160-400MHz DDR I SDRAM
GTL
(Gunning Transceiver
Logic)
2.5V
3.3V
JEDEC
JESD8-3
200MHz Backplane
GTL+ 5V JEDEC
JESD8-3
133-200MHz Backplane
LVDS
(Low Voltage Differential
Signaling)
3.3V ANSI/TIA/
EIA-644
840Mbps Signal transmission
LVPECL
(Low Voltage Positive
Emitter Coupled Logic)
3.3V
2.5V
ANSI/TIA/
EIA-612
840Mbps SONET/SDH,
Ethernet,1394
CTT
(Center-Tap-Terminated)
2.5V
3.3V
JEDEC
JESD8-4
200MHz Backplane-bus
PCI
(Peripheral Component
Interconnect bus)
3.3V     66MHz PC
PCI-X 1.0 3.3V     133MHz PC
AGP 1x, 2x
(Accelerated Graphics
Port)
3.3V     66-133MH Image processing


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.

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