I2C Speed

[Najim]

Hey there,

I wrote a similar thread some time ago and i didn t have any answer, so i try again

I m trying to communicate with PICs via the I2C protocol. The problem is that thay are 20meters(so many yards :P) away from each other. So i have a lot of parasit capacitances...
I would like to communicate with a lower speed than 100KHz with a 20MHz crystal, is it possible?

thank you for your information.

[Hamlet]

oooossorry!

I cant help you.... Instead I will ask help from you!

Im still a newbie at programing and PICs, and in the last quiz at school the teacher asked: define in few words the I2C.

No one in the class could answer.... could you do it for me?

Thanks

[Dave]

Hamlet,
I2C (Inter-Integrated Circuit) Bus

Dave Purola,
N8NTA

[Najim]

hey Hamlet,

Have you looked for it on google? you will find a lot of explanations.

good learning.

[arniepj]

If you can get hold of this IC it could solve your problems.I played with them a few years back and they worked fine.
DESCRIPTION
The P82B96 is a bipolar IC which creates a non-latching,
bi-directional, logic interface between the normal I2C bus and a
range of other bus configurations. It can interface I2C bus logic
signals to similar busses having different voltage and current levels.
For example it can interface to the 350 􀀀A SMB bus, to 3.3 V logic
devices, and to 15 V levels and/or low impedance lines to improve
noise immunity on longer bus lengths.
It achieves this interface without any restrictions on the normal I2C
protocols or 100 kHz clock speed. The IC adds minimal loading to
the I2C node, and loadings of the new bus or remote I2C nodes are
not transmitted or transformed to the local node. Restrictions on the
number of I2C devices in a system, or the physical separation
between them, are virtually eliminated. Transmitting SDA/SCL
signals via balanced transmission lines (twisted pairs) or with
galvanic isolation (opto-coupling) is simple because separate
directional Tx and Rx signals are provided. The Tx and Rx signals
may be directly connected, without causing latching, to provide an
alternative bi-directional signal line with I2C properties.

[Luciano]

Hi,

See also this thread:
http://www.picbasic.co.uk/forum/showthread.php?t=807

Luciano

[Najim]

Thanks both of you!!!!

I heard about those drivers ICs! I m gonna try them and tell u something...
The problem is that I already have designed my card and done it :P Anyway i will try to insert them...

In any case it s a pity that PBP doesn t offer us the possibilitry to change the baudrate...

see ya guys.

[Najim]

Hey guys,


I used the circuit P82B715 with a cable of 14meters long...with a parasite capacitor of around 1nF, and it works very well. The signals are very square!!!

In the datasheet they say, that it can work with a cable with 4nF parasite capacitor...

Najim.

[gluphus]

Najim,

Would you be willing to pm me some of your i2c code? I am attempting to learn the master/slave coding between pics and would appreciate seeing (parts of) working examples.

thank you.