how its possible to insert informations in a bus I2c.

[CHESS]

p90ce201 problem

i have a problem
i need to solve a question : how it's possible to insert informations in a bus I2c.
When bus is in fonction, the microcontroller is dialing with all circuits that have I2c , if i want to ask with a circuit, how can i do ?
The microcontroller don't know me, i dont have adress II2.
When differents circuits want to ask to the bus they have to put the bus in that way "0" or "1" i don't remember exactly and after they can talk to the micro. I want to ask to circuits , to execute a command , and i don't want that the microcontroller know's me.
???

 

[shawndaking]

i2c

you need to gain ownership on the bus by arbitrating it.

when you will gain ownership yuo can write or read to any device on the bus.

 

[Antharax]

Perhaps you should read the I²C-bus specification.
h**p://w*w.semiconductors.philips.com/buses/i2c/facts/

It depends on what type the other microcontroller is (Hardware I²C or Software). If hardware you should try to win bus arbitration. If software there's a big chance that the µC doesn't take into account whether there are other masters (I didn't in my designs ;-)) I guess, in that case, the µC is only transmitting a clock on the SCL wire when it has data to transmit. If it isn't too frequent you can send your data when he's silent.

I hope it helps (I'm not sure i understood the problem)

Antharax

 

[CHESS]

Maybe its not easy to understand
I have an tv set that dials with a lot of ci's
i need only to talk to one circuit , i want him to do a command that's all.
the type of micro is per force hardware
the type is family p90ce201
i don't want a complicate solution

 

[Antharax]

In that case you just need to know the adress of the component. (should be easy to find in the datasheets from the component. When it's adjustable you could use a multimeter to detemine the extra bits on the chip)

Just send I²C data over the wire. (I guess you're gonna do it with another µC??)
You can check with a scope whether there's always a clock on the SCL-wire.

If not, generate your own and send some data in the meanwhile.

First a start condition.
Next the first byte (adress of the component)
Wait for a ack
Next byte
....

This is how the I²C bus works (I got some I²C code or a link for 8051 µC)


If the other µC is always generating a clock it might be a bit more difficult.
*When he allows arbitration for the bus you could try to gain busmaster access.
*You could try to send data as a slave (just use a µC that's fast enough)
*You could always use a PLL to lock on the SCL signal and use a divider in it's feedback loop. In that way you generate a clock signal for your microcontroller that's a multiple of the SCL signal. It's now easy to send data when the other µC is not using the bus.