Difference Between Serial And Parallel Interface?

[voyager2]

Whats the difference between Serial interface and Parallel interface?
I *think* serial connects directly to UART?

[waltr]

Generically to transfer data, say 8bits:
 parallel requires 8 wires, one for each bit of the data so that all 8bits are sent at the same time.
 serial requires only one wire and each of the 8bits is send one at a time.

If you are speaking of specific interfaces such as on a PC then the generic definition holds but there are additional definitions.
So, on a PC the parallel interface is usually called the" Printer Port" and was originally for a Centronics Printer (google it for the details).
A serial interface of a PC was originally RS232 (again google it for details) for connecting MODEMs.

Both of these interfaces has evolved but should be back-ward comparable with older equipment.  

I *think* serial connects directly to UART?

It may or may not. To answer this I need to know exactly what "serial" and what UART you need to connect. Look up the RS232 details and you'll see what the voltage levels are and what the logic levels are for one's and zero's. Then look at the data sheet for the UART and see what its voltage and logic levels are.

If you wish to connect the UART from a uProcessor to the COM port on a PC then you need a level translator circuit between them. The common IC to use is the MAX232 or MAX3232. There are many posts here on SoR on serial interfacing a uprocessor and PC. Also look at the SoR tutorials for how to do this.

Does this answer your questions?

[Conscripted]

Generically to transfer data, say 8bits:
 parallel requires 8 wires, one for each bit of the data so that all 8bits are sent at the same time.
 serial requires only one wire and each of the 8bits is send one at a time.

Does this assume a common ground between the two? I thought you needed two wires for serial.

Conscripted

[waltr]

Yes, a common ground is required for any circuits.

That why I2C is called a two-wire interface, it has SDA & SCK, the ground reference is assumed.

But yea, I probably should have explicitly stated the need of the ground reference in a post to a beginner.

[voyager2]

I think I understand.
Parallel interface needs one wire for each bit plus ground.
Serial interface can communicate with one wire plus ground.
Serial would be slower,  right?

[waltr]

If the clocking rate is the same, then yes, serial would be slower.

Disclaimer: Just so I don't make an over generalized statement that is not always true.
But it is easier to control the impedance of a wire pair than multiple wires so there are serial protocols that are faster than their parallel equivalent. The clocking can be much faster.  PCI Express Bus and SATA are faster than the older PCI and IDE busses.

[Admin]

Although parallel is faster, no one uses parallel anymore for hardware reasons. Just pretend it doesn't exist and spend your time studying serial.

There are many types of serial . . . but these days, when we say serial, we mean 5V TTL.

I predict in 10 years serial will also die, and everyone will only be using wireless and USB.

[madsci1016]

Although parallel is faster

Talking about the 'parallel port' on your computer compared to the 'serial port' this is true.

BUT parallel communication itself is much slower then serial communication. There's a reason all the modern high speed buses (USB, SATA, PCIe) are all moving to serial communication. When you start talking high speed, the extra time a parallel comm channel requires to set up registers with the byte to send, signal a read and wait for ack of receipt, Serial would have pulsed out the 8 bits already.

There's also the mess of making sure each data wire is EXACTLY the right length. if one is too short or too long, the byte traveling down could be misread by the receiver.

Ever look at an old PC motherboard and wonder why there were so many traces that were all squiggly and seem to just take up space? That's why.

[madsci1016]

Also, i was just having a talk with a co-worker who told me that he though back in 2000 that serial (port) would be dead in 10 years.

Yet today i'm placing orders for pc-104 computers with as many serial ports as possible.

I don't ever see serial dying, not while it's still the easiest to use, least overhead, and most versatile.

[waltr]

All wireless digital communications is SERIAL.

[Admin]

You'll still see parallel used when transferring huge amounts of data in specialized high-speed systems. But yea, for practical hardware reasons, serial is almost always better.

As for serial being dead . . . the reason why I make this prediction is that many microcontrollers are now starting to have built in USB. USB will be the new serial

Bluetooth spec 4.0 also makes embedding wireless very energy efficient . . .

[madsci1016]

You'll still see parallel used when transferring huge amounts of data in specialized high-speed systems.

You do for old specialized systems. I can't think of any new ones that use parallel. Hell, even SCSI is converting.

[waltr]

USB will be the new serial

Right, that is my point. USB, SPI, I2C, RS232, RS422, CAN, Ethernet, RS485 are all serial. But are not interconnectable.

If you mean TTL level async then say so. Please don't call it just "serial" as all the different protocols are confusing enough for experienced electronics people let alone the beginners who come here for help.