Part Details for DS18S20 by Dallas Semiconductor

Designers need open-drain logic to run at 1.8V at the 1-Wire master IO. Most 1-Wire slave devices cannot run at 1.8V. This application note presents an RD (reference design) of a circuit that translates from a 1.8V 1-Wire master to a 5V 1-Wire slave device. The RD is used for driving typical 1-Wire slave devices. The MAX3394E voltage-level translator is featured in the design.

Designers who must interface 1-Wire® temperature sensors with Xilinx field-programmable gate arrays (FPGAs) can use this reference design to drive a DS28EA00 1-Wire slave device. The downloadable software mentioned in this document can also be used as a starting point to connect other 1-Wire slave devices. The system implements a 1-Wire master connected to a UART and outputs temperature to a PC from the DS28EA00 temperature sensor. In addition, high/low alarm outputs are displayed from the DS28EA00 PIO pins using LEDs.

This application note demonstrates how to make a simple system that monitors temperature and analog voltages remotely. On meeting certain alarm conditions, the system can send SMS messages, which are then converted to email and forwarded to the designated email address.

This document describes a microcontroller-based 1-Wire® master interface for reliable operation of small, medium, and large 1-Wire networks. This is accomplished using careful impedance matching, intelligent (software-controlled) active pullup, and slew-rate control. Software flow charts are included to assist the user in generating the correct 1-Wire timing for reset pulse, presence detect, write one, write zero, and read time slots using any suitable microcontroller. Scope traces illustrate the timing performance of the driver as well as transmission line effects as they appear with long cables.