DS1621 problem

[andys]

I tried to use ds1621 driver but i can not receive any data from the sensor

the main (for use the driver ) is presented below :

[PCM programmer]

Try this CCS example file. It shows how to call the ds1621.c driver:

[Ttelmah]

As a comment, though the data sheet itself does not mention pull-ups, it says 'open drain I/O lines', and refers to the 'bus specification'. Read the I2C specs...

Best Wishes

[andys]

To be honest i didn't see anything about pull-up resistors but i think when we speak about i2c the pull-up resistors are necessary.

Anyway i use the driver and the example(how to use the driver) without resistors and i receive the value :

TEMP:32 and then a strange symbol.

How to remove the strange symbol ?????

[PCM programmer]

[andys]

You are right PCM programmer.

The status is as follow ( an lcd with 2 lines screens is used):

1)If I don’t use pull-up resistors I can not see anything to the lcd displayer.

2)If I use only 1 pull-up resistor connected to SCL I can see at both lines TEMP:32 with a strange symbol at the end.

3) If I use 2 pull-up resistors I receive at the first line TEMP:32 with a strange symbol at the end. At the second line I receive : TEMP:255 with a strange symbol at the end


what is going wrong ????

[temtronic]

You haven't shown us the entire program, but I'm wondering how you're talking to an LCD module using just printf(...).All 2x16 LCD modules need a 'driver'( either the CCS example or the 'flex' one).
Normally printf(..) will send data to the UART( #use rs232(.....)).
Odd looking data on the LCD screen is puzzling to me
... printf("TEMP.(F)-FULL %.1g",value1);

looks like 14-15 characters before value1 is displayed.
I don't know where the semicolon ( after TEMP comes from either!

Please post your entire program,as well as compiler version.
The more you show and tell, the better/quicker we can figure it out !

hth
jay

[andys]

i am using the flex driver

[temtronic]

hmm. add a delay_ms(500); before calling the init_lcd() function.
LCD modules are 'slow' and need some time to get 'organized' before you can access them properly.

hth
jay

[Jim90]

unfortunatelly if i add a
delay_ms(500); before lcd_init();

i received TEMP:255 all the time !!!


What else can i try ?

[Ttelmah]

Temp=255, is what you would get if the device was not on the address the code is trying to talk to.

The DS1621 driver assumes you have pins A0, A1, and A2 all pulled low. You say this is the case, but are you sure?.

Run the I2C bus scanner program from the code library:

<http://www.ccsinfo.com/forum/viewtopic.php?t=49713>

Does it find your device?. What address is it on?.

Do a search on what 'open collector outputs' means:

<http://en.wikipedia.org/wiki/Open_collector>

This is why resistors are required.

Best Wishes

[andys]

The A0,A1,A2 is connected to ground.

When i use the scanner function the only thing which is printed is the start: nothing else. What is going wrong ???

[Ttelmah]

The device is not being seen on the bus.

Something is wrong with the connections, or the chip itself.

Now, 'step back'. You are using a 33J chip. So Same rail to both chips?. 3.3v?. Same GND connected to both chips?. How long is the connection?. Pull up's to 3.3v?.

The "pull up's" are a classic example of not fully reading a data sheet. Manufacturers often don't give you simple 'you must use pull up resistor' type instructions, but instead simply use the technical description 'open collector' (which means the chip outputs have NPN transistors, to pull the line 'down', but the collector of the transistor is left 'open', so you must supply a pull up...). They do refer you also to the I2C bus specification, and reading this part of the reason they don't talk about pull up resistors then becomes explained, since you can use either resistors (for simple busses at relatively low speeds), or 'active pull ups', with transistors accelerating the rising edge on the bus. Lesson is that if reading a data sheet, and they use a term like 'open collector', make sure you go and find out what this actually means. If a reference is made to a particular bus, then you need to read it's data as well. You can't just skip over things in a data sheet.....

Now, the value for Rp (the pull up resistors), depends on your bus capacitance, clock speed used, and the supply voltage. 2.4KR, should be OK, provided you only have a little capacitance on the bus. Hence the question about your connections.

On your connections, _check_. Don't assume that because you have a wire from pinA, to pinB, that it actually connects. Take the time to sit down with a meter, and test that each connection does get physically to the pin on the chip, and then that it doesn't short to the pin next door. 'Old hands' here will often sit down with a meter, and a magnifying glass, doing such tests, and then searching for whiskers between pins as well. It is one of the commonest problems. Even if you are using a manufactured PCB, unless you paid for 'electrical testing' as the final stage of manufacture, assume there _will_ be whisker shorts sometimes....

PCM_programmers test program really is always the starting point for I2C, simply testing for the chip acknowledging on it's address. This is something that all I2C devices are required to do, and until it is seen by this, there is no point in trying anything else!...

Best Wishes