Hello All, Thanks for the replies. (Sorry for any delay in replying - I only logon at intervals).
Everything so far is as I understood it. My problem is that I don't actually understand it properly - but because I am at the point of designing a new system, I need to. On 13 June 2012 02:01, Eloy Paris <[email protected]> wrote: > All 1-Wire devices have this "presence pulse" feature that you mention > -- that's a fundamental part of the protocol, and all slave devices need > to generate a presence pulse right after they detect a reset pulse > generated by the master. My belief is that this statement is not correct - and it is this that has caused the confusion and prompted the original question. See the difference between the DS1990A and DS1990R (both of which are in active production). I have carefully compared the two datasheets, and there is almost no difference - except for these: "Upgrade of DS1990A Guarantees Presence Pulse on Contact" "Presence Detector Acknowledges When Reader First Applies Voltage" "The DS1990R is a fully compatible variant of the DS1990A. In applications where a presence pulse on contact is critical, the DS1990R should be preferred over the DS1990A." Additionally, having watched i-button authentication in action, these devices sit on the bus for a very short amount of time. Is the controller constantly polling every (say) 125 milliseconds? If so, this would suggest I cannot mix an i-button lock on the same bus as my temperature sensors. As a side example, I have seen circuits using a DS2408 as a keypad input. Although I don't intend to implement this (directly), I am bemused as to how it works, bearing in mind I would only press each button for a fraction of a second in quick succession. Again, it would suggest to me that the device sits on it's own dedicated bus, and is polled at a high clock rate. On 13 June 2012 18:31, Eloy Paris <[email protected]> wrote: > This can also be accomplished with the DS18B20 -- you send the Skip ROM > command followed by the Convert T command. It's called simultaneous > temperature conversion. I have never used it but I understand that OWFS > supports it (the DS18B20s must be powered for this to work). This is my current plan - though my (lack of) free time is limiting my progress. As stated, it requires the DS18B20 to be powered, so I have been working on a suitable circuit and pcb. (I have not yet ascertained the best way of how I should deliver the power in, as I have a long bus length, and all the docs suggest that the use of adjacent wires has an impact on communication timing and reliability). Issuing an Alarm Search [ECh] command should simplify my handling of thermostatic control, and thus reduce the data I am transferring. Cheers all, Phil ------------------------------------------------------------------------------ Live Security Virtual Conference Exclusive live event will cover all the ways today's security and threat landscape has changed and how IT managers can respond. Discussions will include endpoint security, mobile security and the latest in malware threats. http://www.accelacomm.com/jaw/sfrnl04242012/114/50122263/ _______________________________________________ Owfs-developers mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/owfs-developers
