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'[maybe OT?] What is I2C? ]['
Hey, maybe this is a bit trivial for some of you, but what the heck is I2C?
Some kind of bus or something I'm assuming? Protocol? Beats me. And how
about RS232? Isn't that just the cable I use to connect my printer to my
computer? All I could guess is it's some kind of parallel protocol?
Local time : GMT + 5h30m
ICQ # : 565465
I2C is a 2 wire serial bus, very easy to use.
I have just started messing with it and I have to say that it is very cool.
|> Van: Greg Cormier <WLINK.COM.NP> gcormier
> Aan: MITVMA.MIT.EDUPICLIST
> Onderwerp: [maybe OT?] What is I2C? ][
> Datum: donderdag 28 januari 1999 12:39
No, It's not [OT] ! (see below)
> Hey, maybe this is a bit trivial for some of you, but what the heck is
> Some kind of bus or something I'm assuming? Protocol? Beats me.
I2C is a communication protocol & electrical characteristics description.
It's called IIC, or I2C for better pronounciating. AFAIK It means "Inter
Intergration Communication". It consists outof 2 wires. One for Clock
(single direction) and the other for Data (bi-directional). A third wire
can be added to signal an Interrupt to the I2C-bus master.
I'm using it to store/retrieve data into/from a I2C EEPROM (24C16 - 2k*8).
Other I2C devices are, among others, I/O expanders, Real-time clocks and
> And how
> about RS232? Isn't that just the cable I use to connect my printer to my
> computer? All I could guess is it's some kind of parallel protocol?
No, The cable is just the electrical connection between two devices that
communicate thru the RS232-protocol. The electrical characteristics and
the connectors pin-out are part of the specs too (for example : -3 to -16
is a One +3 to +16 is a Zero).
And it's a _serial_ protocol. The Centronics protocol is the parallel one
(used for the Printer ...)
If you are very curious, you could send you a I2C document (plain text).
|GRAEME SMITH email: freenet.edmonton.ab.cagrysmith
Address has changed with little warning!
(I moved across the hall! :) )
Email will remain constant... at least for now.
Even though I am a relative newbie... I thought I'd try to field this
On Thu, 28 Jan 1999, Greg Cormier wrote:
Well the last words right, they are both protocols, SERIAL protocols to be
exact, but they are HARDWARE protocols, rather than SOFTWARE protocols.
The RS232 standard was originally written for phone companies and other
communications applications that needed a serial interface.
The RS232C standard is the one used by most computers, to talk to modems,
and printers. It assumes that one device is the Data Set, and the other,
the Data Terminal. As such, it has a different pin out when two computers
are talking together than it would if it was a computer talking to a
The cable that connects two computers together, has a few twists in the
wires meant to associate the DATA SET signals with the DATA TERMINAL
signals on the other end of the cable, we call this a modem eliminator,
because it essentially allows us to eliminate the two modems that might be
otherwise needed to make the serial connection.
The I2C bus, is a serial bus, based in a shared data line, and a system
clock. It was first designed by Phillips for Television sets believe it or
not, but has been used for a lot of stuff since.
The bus, assumes at least one master device and some slave devices.
pull up resistors are required because the connection is often directly
between devices. Coordination of the bus, is dependent on the MASTER
Device, which also supplies the serial clock signal. A companion set of
software standards, defines how the two types of devices interact.
In short, the main difference between the RS232 interface and the i2C bus,
is that the i2c bus requires some 6 or 7 less lines to impliment.
Hmmmm. Neato. So I2C is just the bus? Are any "commands" or something
defined, or is that up to the components? And I guess it's an open
collector type deal. But I'm assuming you can have more than 1 device on
it, which means addressing, which means there must be a protocol. Sounds
complicated :) What are the practical speed limits on the bus?
Local time : GMT + 5h30m
ICQ # : 565465
|From: pic microcontroller discussion list
> Hmmmm. Neato. So I2C is just the bus? Are any "commands" or something
> defined, or is that up to the components? And I guess it's an open
> collector type deal. But I'm assuming you can have more than 1 device on
> it, which means addressing, which means there must be a protocol. Sounds
> complicated :) What are the practical speed limits on the bus?
A lot of things are fixed with the I2C protocol.
* device addressing
* RAM / register location addressing
* reading / writing a value from / to the RAM-cell / register
You can have standard routines
that work with every I2C-device.
device ist in the range of 0x01-0xFF, where the upper nibble of
the device address is preassigned to different device types.
So normally you can have up to 8 devices of the same type
on the bus (the lowest address bit is used for read / write).
address is either 7bit or 10bit long, depending of the protocol variant
you are using.
value is 0x00-0xFF.
Philips is the inventor of I2C and has good information material.
Dr. Wolfram Liebchen ffo.fgan.deliebchen
Forschungsinstitut f|r Optik
Tel: ++49 7071 709-158
Fax: ++49 7071 709-270
yes, it's a serial bus, and very cunning too.
Using just two open-collector driven signals (SCL and SDA)
it can provide a "micro area network".
Being open-collector driven, if two devices try to drive
a signal to different levels then no damage will result.
The low level will always win out. This fact is used
for bit-by-bit non-destructive arbitration.
And for slaves to make the master wait (by holding SCL low).
Get your I2C knowledge from the horse's mouth (the Philips doc),
read it carefully, and understand it yourself because I have seen
a lot of people misunderstand important features of I2C,
and mis-advise others via the net.
"The I2C bus is a two-wire serial interface developed by the Philips
Corporation. The original specification, or standard mode, was for data
transfers of up to 100 Kbps..." Look in your PIC chip Spec manual under SSP.
Otherwise hit the Web page. It seems to me that the PICs (16C6x &7x) only
support detection of start condition, stop condition and "this is my address."
But does not support the data communications in hardware, is this right.
By the way RS-232 is a communications protocall specifications. It
discribes what each of thoses 25 pins on a "RS-232 connector" do.
At 16:51 01/28/99 +0100, Wolfram Liebchen wrote:
>From: pic microcontroller discussion list
>> Hmmmm. Neato. So I2C is just the bus? Are any "commands" or something
>> defined, or is that up to the components? And I guess it's an open
>> collector type deal. But I'm assuming you can have more than 1 device on
>> it, which means addressing, which means there must be a protocol. Sounds
>> complicated :) What are the practical speed limits on the bus?
>A lot of things are fixed with the I2C protocol.
> * device addressing
> * RAM / register location addressing
> * reading / writing a value from / to the RAM-cell / register
>You can have standard routines
>that work with every I2C-device.
>device ist in the range of 0x01-0xFF, where the upper nibble of
actually, the lsb(it) of the address is the "direction," telling the
addressed slave whether it's a read or a write command. therefore there are
only 126 devices addressable (there's one broadcast address).
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