Re: 1-wire to USB converter that can use 1820s directly

[Marc F Hult <MFHult@xxxxxxxxxxxxxxxxxxxxx>]

Here's one of the pertinent Application Notes
" Guidelines for Reliable 1-Wire Networks" :
http://pdfserv.maxim-ic.com/en/an/app148.pdf

It begins:

"INTRODUCTION
The 1-Wire® protocol was originally designed (many years ago) for
communication with nearby devices on a short connection?a way to add
auxiliary memory on a single microprocessor port pin. Customers soon devised
unique applications that involved extending the bus and moving the slave
devices farther and farther from the master. Problems came up as the bus
lengths exceeded both the capabilities of the bus masters and the limits of
the protocol. 1-Wire device designs responded to the call with added
features and protocols, multidrop (networking) capabilities, durable steel
containers (iButtons®), and mechanisms to assure valid data transfers even
in severely intermittent contact situations.Despite this evolution, 1-Wire
components still perform poorly when bus masters are improperly designed or
implemented, or when masters intended for short line use are pressed into
service with greatly extended buses.

A 1-Wire network is a complex arrangement of devices, wire, and connections.
Every network is different, often in both topology (layout) and hardware.
Various claims have been made about 1-Wire network length and loading
limitations, but the context may have often been unclear. As a result, users
have sometimes been surprised when topologies fail despite the assumption
that they are within specification. Special bus masters have been devised
and tested with a single network design only to find that they are
unsuitable for use in other layouts."

A significant proportion of folks wiring up a whole house full of 1-wire
devices with a single channel will find that they would have saved time,
money and aggravation by reading and understanding the words above and
designing and implementing accordingly.

HTH ... Marc
Marc_F_Hult
www.ECOntrol.org