Problems with 1-Wire DS2438 and PIC16F88

[Darrel Taylor]

OWOUT DQ_Pin,1,[$CC, $BE, $00] ' Skip ROM search, send Convert V, Read page 00h
OWIN DQ_Pin,2,[voltage.lowbyte, voltage.highbyte] ' Read two bytes

$BE is the Read Scratchpad command. (just a comment prob)

The Read Scratchpad command always starts reading at address 0 of the selected page.

The first 2 bytes of page 0 are STATUS/CONFIGURATION and TEMP LSB.
The STATUS/CONFIGURATION defaults to 1's, which is probably what you're seeing.

The Voltage value is at addresses 3-4, so you'll need to read at least 5 bytes to get to the Voltage.

<img src="http://www.picbasic.co.uk/forum/attachment.php?attachmentid=3415&stc=1&d=124285359 2">

[Darrel Taylor]

Here's an easy way to read the whole page ...

Using a technique shown here (Typcasting Variables inside of Arrays)

<font color="#000000"><b>DSbuffer  </b><font color="#008000"><b>VAR BYTE</b></font>[<font color="#800000"><b>9</b></font>] <b>BANK0</b>
<font color="#008000"><b>ASM
</b></font><font color="#000080">DSstat    = _DSbuffer      </font><font color="#0000FF"><b><i>; byte
</i></b></font><font color="#000080">DStemp    = _DSbuffer + 1  </font><font color="#0000FF"><b><i>; word
</i></b></font><font color="#000080">DSvolts   = _DSbuffer + 3  </font><font color="#0000FF"><b><i>; word
</i></b></font><font color="#000080">DScurrent = _DSbuffer + 5  </font><font color="#0000FF"><b><i>; word
</i></b></font><font color="#000080">DSthres   = _DSbuffer + 7  </font><font color="#0000FF"><b><i>; byte
</i></b></font><font color="#000080">DScrc     = _DSbuffer + 8  </font><font color="#0000FF"><b><i>; byte
</i></b></font><font color="#008000"><b>ENDASM

</b></font><b>DSstat    </b><font color="#008000"><b>VAR  BYTE  </b></font><b>EXT </b><font color="#0000FF"><b><i>; Status/Configuration
</i></b></font><b>DStemp    </b><font color="#008000"><b>VAR  WORD  </b></font><b>EXT </b><font color="#0000FF"><b><i>; Temperature
</i></b></font><b>DSvolts   </b><font color="#008000"><b>VAR  WORD  </b></font><b>EXT </b><font color="#0000FF"><b><i>; Voltage
</i></b></font><b>DScurrent </b><font color="#008000"><b>VAR  WORD  </b></font><b>EXT </b><font color="#0000FF"><b><i>; Current
</i></b></font><b>DSthres   </b><font color="#008000"><b>VAR  BYTE  </b></font><b>EXT </b><font color="#0000FF"><b><i>; Threshold
</i></b></font><b>DScrc     </b><font color="#008000"><b>VAR  BYTE  </b></font><b>EXT </b><font color="#0000FF"><b><i>; CRC</i></b></font>

Then you can read page 0 like this ...<table><tr><td>

<font color="#008000"><b>OWOUT </b></font><b>DQ_Pin</b>,<font color="#800000"><b>1</b></font>,[<font color="#800000"><b>$CC</b></font>, <font color="#800000"><b>$B8</b></font>, <font color="#800000"><b>$00</b></font>] <font color="#0000FF"><b><i>' Skip ROM search, Recall Memory page 0
</i></b></font><font color="#008000"><b>OWOUT </b></font><b>DQ_Pin</b>,<font color="#800000"><b>1</b></font>,[<font color="#800000"><b>$CC</b></font>, <font color="#800000"><b>$BE</b></font>, <font color="#800000"><b>$00</b></font>] <font color="#0000FF"><b><i>' Skip ROM search, Read page 0
</i></b></font><font color="#008000"><b>OWIN  </b></font><b>DQ_Pin</b>,<font color="#800000"><b>2</b></font>,[<font color="#008000"><b>STR </b></font><b>DSbuffer</b>\<font color="#800000"><b>9</b></font>]<font color="#0000FF"><b><i>' Read 9 bytes</i></b></font>

</td><td valign=top><br><br>Recall Memory added: see next few posts.</td></tr></table>
After reading, all the values will be in the correct variables, with the correct size (word/byte), ready to be used.

hth,

[HeadCase]

Thanks for your help, Darrel! Your EXT methods will be a great help with other projects.

After adding in your code, I noticed that the raw data was still a series of 1's. I switched to a DS18B20 using your suggested code (with slight modification to the one-wire commands) and it worked perfectly.

For kicks, I removed all of the 1-Wire devices and the raw data is still showing 1's. Seems like the PIC is reading the pin's state (pulled up with a resistor) rather than the data coming over the DQ wire. While the wiring and code seem correct and appear to conform with the datasheets, perhaps I'm missing something?

[Darrel Taylor]

Try adding this before the Read command. (after the conversion)

OWOUT DQ_Pin,1,[$CC, $B8, $00] ' Recall Memory page 0

From the datasheet ...

Recall Memory [B8hxxh]
This command recalls the stored values in EEPROM / SRAM page xxh to the scratchpad page xxh.
This command must proceed a Read SPxx command in order to read any page of memory on the DS2438.

hth,

[HeadCase]

That worked perfectly. While I figured the recall function was a bit redundant, after some more studying of the datasheet, it now makes sense. I'll post the complete code and schematic once I've completed the project.

Thanks for your help, Darrel.