Re: OT, anyone tried LM73 I2C?

On Sun, 29 Oct 2006 21:55:44 GMT, PeteS <peter.smith8380@xxxxxxxxxxxx>
wrote:

PeteS wrote:
sdeyoreo@xxxxxxxxxxx wrote:
On Sun, 29 Oct 2006 20:42:46 GMT, PeteS <peter.smith8380@xxxxxxxxxxxx>
wrote:

sdeyoreo@xxxxxxxxxxx wrote:
On Sat, 28 Oct 2006 23:08:18 GMT, PeteS <peter.smith8380@xxxxxxxxxxxx>
wrote:

sdeyoreo@xxxxxxxxxxx wrote:
Using a BasicStamp to read from LM73 using I2C, but just getting all
1s. Have used I2C before for memory IC and PCF8574 bus expander, OK
but nothing from the LM73. Has anyone had sucess?
I have used this device in multiple designs and it works fine. I
suggest looking at your I2C code.

Cheers

PeteS
Hmm... I have pull ups on both SDA and SCLK lines. Does SCLK need a
pullup? Did you set the pointer register before reading the temp? Did
you use an internal address along with the devices's slave address?
The spec says it powers up pointing to the temperature register, so I
give it the slave address byte and then read back the temp. But
nothing but 1s. I haven't put a scope or analyzer on it yet to see
whats up.
If your familiar with PBasic, here's code:

LM73read CON %10010011 ' I2C address
I2Cpin CON 0 ' P0->Sdata,P1->SCLK
tempIn VAR Word ' 16 bit word from LM73

' read 2 bytes (16 bits) from LM73 into WORD tempIn:
I2CIN I2Cpin,LM73read,[tempIn.HIGHBYTE, tempIn.LOWBYTE ]

The required pullup in I2C depends on the capacitive loading of the
bus, and yes both SCK and SDA should be pulled up for standard
devices. What value pullups do you have? An incorrect pullup value
will certainly make things fail at fullspeed.

Cheers

PeteS

4.7K pull-ups. The circiut is only that device built on a uController
development board I've used for other I2C.
What language did you use? Could you post a relevant snippet?

I don't have any code here, but I've run I2C controllers in C, C++ and
various assembly languages.

What controller are you using? 4.7k seems somewhat high for I2C pullups
- I usually use about 2.2k for a single device (which goes down as more
devices are hung off the bus) but it depends on the controller spec.

Cheers

PeteS

I will note that I had problems with this device the first time I used
it because the pullups were too large.

Something else for you to check: Is the device an LM73-0 or LM73-1? Is
the address pin grounded?

A simple test is to use all the available addresses.

The LM73-0 has base addresses of:

1001 000[RnW] A = Float
1001 001[RnW] A = GND
1001 010[RnW] A = VDD

the LM73-1 has:

1001 100[RnW] A = Float
1001 101[RnW] A = GND
1001 110[RnW] A = VDD

At least it's a test you can do easily.

Cheers

PeteS

I'm using a BasicStamp (a Ubicom SX48AC ). We have a bunch we use as
quick and easy controllers. We test various ICs, A/Ds, D/As, these
temp sensors, DDSs CMOS analog switches, EEPROMS,... We find these
BasicStamps very quick and easy, but I've thinking of switching to
PIC16F876A and using PicBasicPro for the language. Propably try this:
http://www.melabs.com/products/bundles.htm#X2 from Melabs.
My device is a -0 so addrss should be 001 (with add gnd).
One thing is it's hard to tell pin 1, there's no dot or beveled edge.
Devices are maked T730, with pins along bottom and top of marking:ie,
pin 1 under T, pin2 under 7... pin 4 under 0, pin5 over 0, ... pin 8
over T ?

Tomorrow I'll try 1 k pullups, connect a logic analyer, see whats up,
see if it's even clocking...
.