I2C/DS1631 question

[milkman41]

I'm using a PIC16F877A, and a DS1631 temperature sensor through I2C. I'm wondering if I can add another DS1631 on the same pins, like piggyback it on n whatnot, and then get the temp from both. I've used the one-wire sensors like the DS1820, and I know you can do that to them (at least on the board I used), so I want to know if I can do it with the DS1631. If I can, could anybody point me towards some helpful code?

Thanks,
-Nick

[stewart]

Milkman45,

After a quick look at the data sheet, if you have one talking, then is should be a simple matter of getting 7 of them on the same bus.

In the back of my mind I wonder how you have one working and still be asking this question?

from the data sheet

[rnielsen]

As you look at the data sheet it talks about the 2-wire communications. The control byte is configured as:

1 0 0 1 A2 A1 A0 R/W

A2, A1 & A0 correspond to the A2, A1 & A0 pins on the part. This will enable you to have multiple parts on the same bus. If you have all of the address pins (A2-A0) tied to ground then the control byte will be:

1 0 0 1 0 0 0 R/W

This should allow you to talk to up to eight devices individually.

Ronald

[Ttelmah]

Actually 8 (three address bits). Addresses are 1001xxx.

The supplied code, is for the three bits all set to '0', addresses 0x90, (and 0x91 for reading). All that has to be done, is to change the four points where this is used in the supplied code, to use a variable instead. So, in the init_temp code, and temp_config code, instead of I2C_WRITE(0x90), use a variable here. Similarly in the read_full_temp, and latter where '91' (the read address) is used, substitute the value in the variable+1.
Set the variable to the value for the chip required, and call the code as is currently done.
Then add the extra chip, and set the input pins to match the new address selected. So with A0=1, use address 0x92.
Reading the data sheet, is the best place to start. This paragraph "says it all".

"Every slave device on the bus has a unique 7-bit address that allows the master to access that device. The 7-bit bus address is 1 0 0 1 A2 A1 A0, where A2, A1, and A0 are user-selectable through the corresponding input pins. The three address pins allow up to eight DS1621s to be multidropped on the same bus"...

Best Wishes

[stewart]

Ttelmah

Yes of course, I was thinking "7 more".

Thanks for clearing up the confusion my simple error might have created

Stewart

[milkman41]

I probably should have mentioned that I am pretty much a total n00b (:p), and that alot of this goes whooooosh over my head, haha, but thank you for the suggestions, I will look into it, and see if I can't figure something out.

Also, the way I got the first one to work was cuz I got the development kit and it has an example for the DS1631, so yeah. But I will try to implement what you guys have told me, thanks again.

-Nick

[milkman41]

[stewart]

Time to get out the data sheet and do some "light" reading:
http://datasheets.maxim-ic.com/en/ds/DS1631-DS1731.pdf

Open the hymnal to page 11 of 15.

The high half is always 1001 (9 in HEX)
D3.D2.D1 is the address of the device you want to talk to.
D0 is the R/W bit 1=Read 0=Write

If you want to play in this sand box, you have to do some reading and playing.

So the address pins on the chip are marked A2, A1, A0, and all are grounded, then the chip's address is 000 or 0.
if A2 = 0, A1 = 0, A0 = 1, that is 001 or 1
if A2 = 0, A1 = 1, A0 = 0, that is 010 or 2
if A2 = 0, A1 = 1, A0 = 1, that is 011 or 3
if A2 = 1, A1 = 0, A0 = 0, that is 100 or 4

and so on.

The confusing part is that in the control word these 3 bits are shifted to the left by the R/W bit.

Hope that this helps, you don't have to read and understand the entire data sheet, but do take a look at the area of need.

Have fun, play with it.

Stewart

[Ttelmah]