Re: OT, anyone tried LM73 I2C?

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
.

Relevant Pages

  • Re: OT, anyone tried LM73 I2C?
    ... 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. ... 1001 001A = GND ... 1001 010A = VDD ...
    (comp.arch.embedded)
  • [PATCH 7/35] W1: feature, enable hardware strong pullup
    ... Add a strong pullup option to the w1 system. ... The one wire bus requires at a minimum one wire and ground. ... The hardware USB 2490 one wire bus master has a bit on a few commands ...
    (Linux-Kernel)
  • Re: [PATCH 5/30] W1: feature, enable hardware strong pullup
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  • Re: Pull up resistor
    ... One thing to watch out for is when the pullup is on a bus (such as I2C ... / SMBus). ...
    (sci.electronics.basics)