Choosing a bus for controlling 20 pic12 50mm apart

[exapod]

Hi,
some time ago i made a small board with a pic12 controlling one rgb led.
Now i have some boards left (more or less 20 ) and i would like to connect the boards in one bus and be able to control them.
I have two i/o left on the pic12.
The distance between two board should be no less than 50mm ( 1m in total).
What kind of bus should i use?
I was thinking i2c but i don't know if the lenght of the cable can be a problem.
Thanks for the help

[jb79]

Hi!

1m should be possible.
It's important that the capacity of the bus doesn't go over a certain level. Otherwise the rise time (0=>1) would be to high for the system.

There are several ways to solve such problems:

lower bus speed i possible
bus bridge/repeater to split the bus into two or more shorter segments
...

The best idea would be to try it with 2 or 3 of your boards connected to a 1m cable.

best regards
Juergen

[fcb]

Quite possible to do without any buffering/extra components - but will depend on speed (bus capacitance and ground noise).

[exapod]

I will try and let you know. Any advice on the type of cable ?
Sorry for the late response.

[Christopher]

How aboout an i2c serial interface?

Each pic is a master as well as a slave, only responds to data with its own address then shoves all the rest out to the next pic?

This way you may not need to have a buffer on each chip

[exapod]

How aboout an i2c serial interface?

Each pic is a master as well as a slave, only responds to data with its own address then shoves all the rest out to the next pic?

This way you may not need to have a buffer on each chip

I can't do serial i2c because i have only two i/o left.
I took a quick glance at this appnote: http://www.maximintegrated.com/en/app-notes/index.mvp/id/148 and it seems that i can use the 1-wire protocol.
Later i will read it more carefully and maybe do some tests.

[Christopher]

I have used the p82b96 i2c bus buffer successfully over a few m,