I2C timeout for master

[Ringo42]

I'm using an 18F452 that talks I2C to other devices. I was testing with nothing attached and noticed that with no slave attached the master locks up when it tries to write.

Here is the relevant code
#use I2C(master, sda=PIN_c4, scl=PIN_c3,slow)

i2c_start(); // restart condition
i2c_write(address);//address
i2c_write(16);//P is 16th letter
i2c_write(20);//pwm
i2c_write(0);//dir
i2c_write(20);//pwm
i2c_write(0);//dir
i2c_stop();

Is this normal? If so is there an easy way to make so I can test with nothing attached?

Thanks
Ringo
_________________
Ringo Davis

[PCM programmer]

You probably don't have pull-ups on the master side. If you have
pull-ups, the master won't lock up with your test code, even though
there is no slave.

[Ringo42]

I'll check tonight. The board is mostly populated, so it is possible I forgot to put them on.
Thanks
Ringo
_________________
Ringo Davis

[PCM programmer]

Or, you might only have pull-ups on the detachable slave board. If so,
you could add some light pull-ups on the master board (such as 10K).
They would pull up the i2c lines when the slave is detached.

[Ringo42]

The pads for the pullups are on my master board, but I might not have populated them yet. I'm assembling and testing at the same time, so I might have skipped over them.
Thanks

Ringo
_________________
Ringo Davis

[xa4]

Greetings,

I have the same problem as Ringo but the pullup resistors (4k7) are present on my master circuit board..

Any ideas ?

Thank you !
_________________
Best,
Xavier Righetti - http://xa4.ch

[PCM programmer]

1. Post the manufacturer and part number of the i2c chip that you are using.

2. Post a link to a schematic of your board (if possible).

3. Post a very small program that shows the problem.

4. Post your CCS compiler version.