The parallel interface describes a digital input or output of a computer or a peripheral device . When transmitting data via a parallel interface , several bits are transmitted in parallel , in contrast to the serial interface , in which the bits are transmitted one after the other.
With regard to peripheral devices, a “parallel interface” nowadays usually means a connection according to IEEE 1284 , which after its use is also referred to as a printer interface or printer port (English line printing terminal , LPT for short); usually the port number was appended to it, for example LPT1 or LPT2. The LPT interface has 25 pins.
Initially, only unidirectional communication with devices was possible ( Centronics interface ), which limited the application to printers or special drivers for individual applications such as e.g. B. Scanner required. In contrast, the IEEE 1284 standard from 1994 also included bidirectional data transmission via the parallel port and thus As the connection of corresponding CD-ROM drives and CD burners , the computer and printer looped were. The achievable data rate is 2 MB / s per direction, when using at least the EPP mode.
With the development and good availability of devices for USB from around 1999 (USB1.1) and FireWire , parallel interfaces are practically only used for older peripheral devices or by older computers and are therefore considered to be obsolete interfaces. legacy port , led.
Control modules for parallel interfaces
The link between for the connected peripherals and used in the device microprocessor or microcontroller is a specially optimized for this application module that mostly as a PIO (English: p arallel i nput / o utput) or PPI (English: p rogrammable p eripheral i nterface) referred to as. In addition to controlling the data transmission and buffering the data, its most important tasks often include adjusting the signal level. Blocks for parallel interfaces can be found in many forms and variants. Depending on the manufacturer, the connection diagram of the components was such that they could be easily adapted to a specific processor family, usually that of the manufacturer, for example Zilog ( Z80-PIO for the Z80 -CPU) or Intel ( 8255 for the 8080 / 8086 family ).
Board level standards
- VMEbus for industrial computers based on 68xxx from Motorola and Philips
- NuBus bus system from Apple , NeXT and TI
- ATA bus PC bus system based on 80xxx (predecessor of the PCI bus)
- ISA bus (XT or AT bus)
- PCI and AGP bus
- Europe Card Bus and DENYS
Communication with cable lengths 0.1–20 m
- ATA / ATAPI for hard disk and CD / DVD drives
- SCSI for hard drives, scanners , CD / DVD drives
- IEC-625 bus , HP-IB or IEEE-488 for measuring devices, plotters, printers
- IEEE 1284 , EPP , ECP -Centronics printer interface