Parallel Connections

Michael Fromwiller

CS 147 Spring 08

Dr. Sin-Min Lee

Parallel Interfaces

Buses transfer data inside computers.

Monitors, printers, and other devices do not connect to the system bus.

External devices connect to interface circuits which are used to manage the connection.

Proper connections require the ability to send and receive data.

Centronics Printer Interface

Multi-wire parallel link.

Transfers 8 bits of ASCII code simultaneously.

Typical speed: 100 kbytes/sec over10 meters.

Not considered a bus– Does not offer support for more than two

devices.

Centronics Printer Interface

Up to 8x faster than serial connections!

… but suffers from “skew”

Differences in wire resistances

+

Lots of wires

Signal degradation, delays, and

data corruption. Yuck.

                      

                      

Low Skew

High Skew

Centronics Printer Interface

Three standards for this interface:

Mode Name Speed I/O Controller

SPP Standard Parallel Port

100 kbytes/s

Output Software Controlled

EPP Enhanced Parallel Port

1 Mbytes/s

Output & Input

Hardware Controlled

ECP Extended Capability Port

5 Mbytes/s

Output & Input

DMA w/ FIFO

Standard Parallel Port (SPP)

Software handles connection (slow)Host sends important data (a print job, for

example) to device.Device sends status messages to the host:

– Accepting data– Busy, try again later– Out of paper– Error found

Typical setup between devices for asynchronous handshaking.

EPP and ECP Modes

Both offer bi-directional lines for data communication between device and host.

Important for Plug-and-Play process.

Hardware handles data transmission– Software writes data to port buffer– Hardware handles the rest (fast!)

SCSI - Small Computer Systems Interface

Fast asynchronous byte-wide bus(5 Mbytes/sec) connecting up to 8 devices

A secondary bus which relieves the traffic from the main bus.

Intended for:– Hard disk drives– CD-ROM drives– Tape units

SCSI - Small Computer Systems Interface

Variations of SCSI standards:– Fast SCSI

• (10 Mbytes/sec synchronous transfer mode)

– Wide SCSI• (40 Mbytes/sec with 32 bit data bus)

Useful for:– Multiple computers with shared drives– Multiple CD-ROM burners for mass production– Tape drives

IDE – Intelligent Drive Electronics

Simplified version of the ISA bus.

Standard was quickly accepted.– Used by cheapest hard disk drives– Used by most common hard disk drives

Ribbon connections support two devices:– Master– Slave.

Plugs directly into the AT bus.

AT / ISA bus

Appeared around the time the Intel 8088 processor came out.– Ran at 4.77 Mhz– Later topped off at 8.33 Mhz

Faster processors would wait till the ISA bus was finished, affecting speed.

Pentium CPUs made the speed difference clear.

Extended ISA (EISA) clocked at 33 Mhz, but was overshadowed by the new PCI bus.

PCI – Peripheral Component Interconnection

PCI bus isolated from main bus by a “bridge” device, such as the i82443.

“North Bridge” – Handles PCI components

“South Bridge”– PCI to ISA bridging device, such as the i82371

Development of the mini-PCI was brought about by laptop computers, for PC add-ons.

PCI – Peripheral Component Interconnection

PCI bus operates in two modes:

– Multiplexed Mode• A single 32 bit bus that is shared by address and data

information.• Increased bus width, but reduced data rate.

– Burst Mode• Same idea as EDO DRAM. After one address has

been sent, several data items follow in quick succession.

• Bridge is capable of assembling these “packets” of data and bursting it to the PCI bus when ready.

Plug-and-Play

Introduced by Microsoft.Main purposes:

– Allow computer to auto-configure hardware.

– Simplify hardware installation.– Make the PC more user friendly …

“Released” with Windows 95.Fully supported by Windows 2000/XP.

PCMCIA – Personal Computer Memory Card International Association

Credit card sizedOriginally intended for memory expansion

for laptops.Designed for “hot swapping.” No need to

turn off or reboot laptops. Just pop and go!Manufacturers took it a lot further:

– Modems and Ethernet interfaces– Video cards– Parallel ports– Disk drives– Pretty much anything!

Sources All information from this presentation can be found in:

Computer Systems Architecture – A Networking ApproachRob Williams. Chapter 11

“Low and high skew” images:– http://www.spectra-strip.amphenol.com

“Parallel printer cable” image:– http://www.nuggetlab.com/comptia_files/equipment/

cable_Parallel%20Cable%20showing%2025-pin%20end.jpg “SCSI ribbon cable” image:

– http://www.qvs.com/prodimages/SCU160-4T_LR.jpg “IDE ribbon cable” image:

– http://www.cable-house.com/images/cables/internal%20cables/ide_ata133_ribbon_cable.jpg

“Granny with computer” image:– http://www.boston.com/business/blog/filter/momtechsupport.jpg

“PCMCIA card” image:– http://upload.wikimedia.org/wikipedia/commons/b/b1/

Pcmcia-type-ii-and-iii.jpg