One-wire commands

Archiver

Hi group!

The STAMP manual shows a 4.7k pull-up resistor with the DS1820 1-wire
device and makes a casual reference that the OW commands will not work
without the resistor. However, I cannot find any mention of a pull-up
resistor in the iButton or 1-wire documents I've obtained from the
Dallas Semiconductor website. Does anyone know why the resistor is
necessary? I thought the 1-wire devices got their power when the
clock/data line was high... Does the pull-up supplement the Li battery
in the iButton?

--Jeff Wallace

Start data-logging with a RTC, 256k EEPROM and an I2C bus for your BS2
http://www.high-techgarage.com/products/timekeeper.php

Archiver

[font=arial,helvetica]In a message dated 6/7/01 10:48:25 PM Central Daylight Time, bs2web@yahoo.com
writes:

The STAMP manual shows a 4.7k pull-up resistor with the DS1820 1-wire
device and makes a casual reference that the OW commands will not work
without the resistor. However, I cannot find any mention of a pull-up
resistor in the iButton or 1-wire documents I've obtained from the
Dallas Semiconductor website. Does anyone know why the resistor is
necessary? I thought the 1-wire devices got their power when the
clock/data line was high... Does the pull-up supplement the Li battery
in the iButton?

What documents are you looking at? ·I just opened three that I had handy and
all show the 4.7K pull-up on the bus. ·The pull-up is required because 1-Wire
devices have only one other connection: to ground. ·A "0" can be sent by
pulling the bus to ground. ·A "1" is sent by leaving the bus high.

Trust me, you need the pull-up.

-- Jon Williams
-- Applications Engineer, Parallax[/font]