[i2c] MAX1236 with smbus (CS5536 ACB0)

Andreas Seidler tetzlav at leipzig.freifunk.net
Wed Oct 15 03:01:56 CEST 2008

Jean Delvare schrieb:
> Hi Andreas,
> On Mon, 13 Oct 2008 03:20:48 +0200, Andreas Seidler wrote:
>> I want to connect a MAX1236 (ADC) [1] to a I2C/SMBus in a
>> PC-Engines/ALIX board to monitor some voltages.
>> This board have a AMD geode CPU with an an I2C companion (scx200_acb.c).
>> but i cant access the MAX1236 on slave address 0x34.
>> (0x4c is the onbard LM90)
> Maybe it's not wired properly?

I can access this ADC wired to a i2c-ibm_iic (build-in IBM PPC_P405)

> If it is wired properly, then another possibility is that the MAX1236
> is doing clock stretching beyond what the CS5536 supports...

and this is my second problem: i cant read the A/D-converted values from
userspace (eg. with i2cget) without spezial code or kernel module?

>> Does "I2C no" means the CS5536 is a plain smbus without i2c support?
> Yes and no. It means that the scx200_acb driver runs the CS5536 in
> SMBus mode without plain I2C support. But there is also the scx200_i2c
> driver (which I would love to see go away in favor of i2c-gpio but
> that's another story) which can use the same pins as GPIO to do plain
> I2C. 

Thank you for this info!
Know i found "the story" in this thread too (http://lkml.org/lkml/2007/4/14/59)
with more infos.

now i tested scx200_i2c:
root at OpenWrt:/# insmod scx200_gpio
scx200_gpio: no SCx200 gpio present
root at OpenWrt:/# insmod scx200_i2c
scx200_i2c: no SCx200 gpio pins available

(i hope thats no problem of the openwrt-distro...)

are SCx200 GPIO pins supported by i2c_gpio?

should it work with my Geode/LX800 companion?

> If I read the MAX1236 datasheet properly, it uses transactions
> which aren't part of the SMBus set, so you may need to use the
> scx200_i2c driver, depending on what exactly you need to do with the
> MAX1236.

I only want to monitor some voltages in my wind-/solarpower system and draw some
nice charts - nothing spezial.


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