Universal Parallel Bus -- why not?

Yes it would be how ever, that cost more..

Significantly more?

You're 30 years too late. They called it the Parallel Port. Used on everything.

Its fundamental limitations are: 1. attached to the 8MHz ISA bus (baud < ~1Meg/s), cable length or signal quality (limited to about 1 meter), and the cable contains 25 wires = it's a heavy bastard and requires lots of connections = more to go wrong.

I suppose one could make a PCI or PCI-E clocked "parallel port", maybe using LVDS and terminated transmission lines, but then you'd be right back at something like 100MBit ethernet (CAT5 = four parallel pairs).

USB has only four wires. They fit nicely into a robust connector. Can't beat that.

Tim

Against my better judgemnet, since I know GX is just a troll, I will answer his question...

When you have one signal line, and you send a bit, then once you are able to determine the status of that bit, you are ready for the next one. You can do this very quickly.

However, when you have two lines, then you have to be able to know, not just the status of one of those lines, but that of both of them, at the same time. This takes a little longer to be certain, and therefore, it goes slower. One line or the other may be a little longer, or have a slightly different impedance, or any number of other reasons that makes it different. Yes, this is ofen more than twice as long as for a single line.

As you add signal lines, the problem grows. You have to wait till you can be sure that ALL the lines have reached the correct state, before you can move on to the next. Now, you may think that this doesn't grow too fast, and you are right. But, at the same time, your hardware has also increased. Your clock speed has gone down, and your hardware cost has gone up. This makes a parallel signal not very attractive

So, how do you get faster throughput? You use multiple serial lines, like LVDS, each taking a part of the flow, and add them all togther at the the other end.

Charlie

At very high speeds you start to get skew in the prop delay between different data lines of a parallel bus... the bits arrive at the destination at different times. The higher the clock rate and the longer the bus, the worse this problem gets.

A signal traveling over a single twisted pair has no skew problems. And electrical losses/dispersion can be fixed with per-lane adaptive equalizers. For higher data rates, you add more lanes, each with its own transmitter/equalizer/receiver/fifo, and merge the data streams digitally. So long, fast serial busses scale much better than parallel busses. They are smaller and use less connector and IC pins, too.

John

and toggling a wide bus slowly will use just about as much power as toggling a narrow bus fast so theres no magic gain in efficiency

-Lasse

It has. It's often called the "Printer Port".

No. and HELL NO.

Of course, look at the old Centronics port printer cable compared to a modern USB cable.

A common fast parallel bus was the SCSI port for HDDs, and these days they use SAS (Serial Attached SCSI) because it's faster than old parallel form, which went from narrow, wide and ultrawide before going serial to run even faster.

And the reason is as other posters state, data skew between parallel lines limits max data rate. It's faster to go serial. That's why hard drives now use SATA rather than the old ribbon cable.

USB is also self powered, it grew from the serial keyboard connection where the requirement was met by four lines: power, data, clock and ground to get the cheapest hardware solution.

Also, USB's self clocking gets rid of the old serial port's parameter setting issues.

Grant.

Look up IEEE-488

It was an attempted semi-universal parallel bus system. It had several problems. One being that the specs were written by lawyers. They were very hard to understand. There was also one part to do with the serial pole method that was ambiguous. Two systems could comply but not be compatible with each other.

" snipped-for-privacy@att.bizzzzzzzzzzzz" wrote in news: snipped-for-privacy@4ax.com:

because cables for them would be far more complex and costly. How many bits were you considering for your "universal bus"? A 32 bit bus is going to need 32 wire pairs(signal and GND) or 32 coaxial cables of equal length,along with clocks,power and grounds. And now we're at 64 bit buses. Just look at the old printer cables.

TV stations had the same problem when they went to digital video.and they only used a 10 bit bus.

Yes. ..but....more expensive,complex,and more prone to breakage. Also,fewer cables could be run in the same ducts.

MORE energy consumption,because your driver port has to drive all those outputs,instead of a single output.

TANSTAAFL.

No. Skew.

It has been done, twice. IEEE-488 for instruments, and SCSI for small computers.

Expensive cables made IEEE-488 a boutique item, and SCSI (which got up to 320 MBytes/sec) was usually kinda high-end Most Macintosh computers from 1986 to 1998 used SCSI.

Parallel ports DO NOT COUNT, because they aren't a bus; the early ones weren't even bidirectional, and there was never any good support for more than two connections. Bus, from 'omnibus' meaning 'for everyone' implies that all bus signals are served by all devices, not just two.

nope. Serial is faster nowadays. Compare SATA-300 to PATA-133.

Audio equipment like samplers and keyboard workstations also used SCSI, both for sample transfer between a PC and the hardware and for mass storage. Audio manufacturers were quite slow to switch from SCSI to flash memory/USB for storage/transfer; it was possible to buy new equipment with internal or external SCSI-1 ports well into the 21st century. SCSI-1 compact flash readers sell for big money on Ebay for retrofitting older equipment.

Nonsense. You could attach anything you wanted to them. The parallel port on the PC has always been bidirectional.

ALL devices? My PCI bus doesn't serve my memory. You're just making things up now.

te:

l port on

Nope.

things

So are you.

Good point, Charlie...

This is being pushed to it's extreme, with multiple Very High Speed serial busses On-Chip and Off-Chip these days.

My kid is working on simulating these at IBM.. They are around 10 GHz and each serial 'bus' has adaptive transmitters and receivers so the same design can be used for a variety of signal paths without redesign..

The electronics world is getting weird :-)

I got off the BUS just in time...

Pro photographers with Macs?

-- "Electricity is of two kinds, positive and negative. The difference is, I presume, that one comes a little more expensive, but is more durable; the other is a cheaper thing, but the moths get into it." (Stephen Leacock)

The "standard" PC printer port of the PC/XT was the 8255. This chip could go both directions. Later PCs integrated the printer port function into a chip and removed some of the abilities.