One Wire Communication with Maxim/Dallas Semiconductor IC

JDOhio

Greetings,

I am attempting to communicate with a Maxim/Dallas Semiconductor IC DS2438 (Smart Battery Monitor, http://www.maxim-ic.com/quick_view2.cfm/qv_pk/2919). So far, when I attempt the reset, the return code indicates no devices on the 1 wire bus. Here is the SX/B:

OneWireInitialize:
    OWRESET OneWireDQ,OneWireLow0
RETURN

After this executes, the memory at OneWireLow0 contains 3 (no devices on the bus). I have included a schematic.

I have been checking the obvious things like wiring and Maxim/Dallas application notes but so far nothing leaps out. Anything else I might check? Anyone using 1 wire devices? Anyone using Maxim/Dallas 1 wire devices?

How should the port be initialized? I've tried both as an input and an output.

Thanks!

Bean

Just connect Vdd directly to +5V, and +5V through the 4.7K to the DQ line, and the DQ line to the SX pin.

Bean.

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JDOhio

Thanks, Bean! I'll give that a try. I have it wired as shown in the schematic because the documentation indicates that the chip can run off of parasitic power. I should have tried the direct route as you suggested first just to help prove things out.

Joe

Bean

Yes, but parasitic power comes from the DQ line when you don't have +5V available at the device. The diodes and cap are built into the device, you just leave Vdd unconnected.

Bean.

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
“The United States is a nation of laws -· poorly written and randomly enforced.” - Frank Zappa

- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
www.hittconsulting.com
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