Lpc2000

On 7 Sep 2004 at 11:51, Ian Wraith wrote:

> Hello
>       I am currently looking at using a LPC2106 in an access control
> unit to interface to a number of Dallas DS1990 iButtons. Am I correct
> in thinking that with a little code the iButtons could be interfaced
> to any of the LPC2106's GPIO pins ? Or would the iButton need to be
> interfaced to one the processors serial IO pins ?
> 

From a Maxim App-Note:
1-Wire devices operate in an open-drain environment on bus voltages
ranging from 2.0V to 5.5V.  Exact logic levels and minimum pullup
voltages are device dependent, though generally parasite-power devices
require minimum pullup voltage of 2.8V to recharge an internal storage
capacitor used to supply power during periods when the data line is low.
A 4.7k resistor typically serves as the pullup on the 1-Wire data line.
The resistor provides logic-high signals passively, with the bus master
and all slave devices driving the logic-low signals.

Only the pins for the I2C interface are open drain, hence you probably will need
to add a transistor or tri-state buffer type circuit as described in the Dallas/Maxim
app notes.

Regards
   Anton Erasmus-- 
A J Erasmus