I2C Address problem

[bidakung]

I have wired the ds1621 with raspberry pi. When i try this command

Code: Select all

i2cdetect -y 1

then address of I2C device is shown

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     0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f
00:          -- -- -- -- -- -- -- -- -- -- -- -- --
10: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
20: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
30: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
40: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 4f
50: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
60: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
70: -- -- -- -- -- -- -- --

then when i try another i2cdetect command, the address was changed

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     0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f
00:          -- -- -- -- -- -- -- -- -- -- -- -- --
10: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
20: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
30: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
40: -- -- -- -- -- -- -- -- 48 -- -- -- -- -- -- --
50: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
60: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
70: -- -- -- -- -- -- -- --

i don't know why the address was randomly changed(in the range of 0x48 to 0x4f). My code is about to read temperature from a fixed address, sometime it failed to read because of i2c address was changed

[FTrevorGowen]

I have wired the ds1621 with raspberry pi.
...
i don't know why the address was randomly changed(in the range of 0x48 to 0x4f).
...

Random address changes on an i2c device usually occur if one or more of its A0 - A2 address pins have not been connected to 0v or Vcc (ie. logic low or high). In this state the input pin(s) is/are "floating" and its/their logic state can appear to change. If you have made connections, check for poor (dry) joints.
I don't know what the "base address" of a ds1621 should be (ie. that when A0 - A2 are tied to 0v) but, for example, the MCP23017 port expander chip has a base address of 0x20 and, in another forum post was being detected at address 0x20 ... 0x2F IIRC because its address pins were untied.
Trev.