Bit bash I2C slave?

SherpaDoug · Joined: 07 Sep 2003 Posts: 1640 Location: Cape Cod Mass USA

Is it practical to use a PIC like the 16F628A without I2C hardware as a slave? I want to eavesdrop on a SMB data exchange but I don't have any I2C hardware chips on hand. Maybe I should just order some and shelve this project till they arrive?
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kolio · Joined: 06 Feb 2008 Posts: 26

Assuming the application is only to sniff and then send the information via UART. So, it would be a nice exercise if you have the necessary time. And probably you'll never get a dedicated chip flexible enough as 628 is. BTW 628 is my favorite.
Good luck!

SherpaDoug · Joined: 07 Sep 2003 Posts: 1640 Location: Cape Cod Mass USA

Since I will only be a 3rd party sniffing the lines, and I don't want to generate ACK/NACK I suspect the hardware I2C might be a problem. I'll give it an hour and see if I can do it in software with my 628. It would probably take an hour to process a !@#$% corporate purchase order anyway.
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The search for better is endless. Instead simply find very good and get the job done.

rnielsen · Joined: 23 Sep 2003 Posts: 852 Location: Utah

Even with a hardware I2C I'm not sure you would have much luck anyway. The slave would simply sit there, doing nothing, unless it saw it's address being sent. You would need to know the addresses being sent as well. It's, also, not possible to have two slaves with the same address so I would imagine you would need to set up a different kind of 'sniffer'.

A data-logger type of device might be better since they're supposed to just grab whatever signals it's supposed to and stuff the data somewhere for retrieval at a later time. Maybe have an EXT_INT tied to the SCL line and be triggered from that. Not sure though, just a place to start.

Sounds like a fun little project to tackle though. Good luck!

Ronald

PCM programmer · Joined: 06 Sep 2003 Posts: 21708

If you want to spend some money, you can buy a logic analyzer that
has an i2c interpreter built into the application program.

We have this one, the LA1034:
http://www.pctestinstruments.com/
It's a relatively low cost, 34 channel, 500 MHz timing analyzer that
is very compact in size and plugs into a USB port on your PC.

To use the i2c interpreter, you connect two pins to the SDA and SCL
signals, and then it displays another channel that shows the start and
stop bits, the R/W address, and the ACK bits. Here's a screen shot:
http://www.pctestinstruments.com/logicport/interpreters.htm

When we got this unit, we put our old HP analyzer in the closet.

SherpaDoug · Joined: 07 Sep 2003 Posts: 1640 Location: Cape Cod Mass USA

That looks real nice! And the low price keeps it out of the "capital equipment" category. Does it have any logic outputs? The one thing I like about my ancient, noisy, heavy, power hungry HP1630 logic analyzer is that has a trigger logic output BNC, so I can use it to trigger my scope to look at analog characteristics from a complex logic trigger.
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The search for better is endless. Instead simply find very good and get the job done.

rnielsen · Joined: 23 Sep 2003 Posts: 852 Location: Utah

Take a look at this one. It's not fancy but has several protocols it will interface with. http://www.hobbylab.us

Ronald

ivan · Joined: 03 Apr 2008 Posts: 8 Location: Italy Rome

this hobbylab also looks good but is identical to poscope also sw are same look at www.poscope.com difference the last ship from europe(free)
I have LA1034 from 2 years and is wonderful product but if you don't have a real scopemeter or your budget is little the poscope is best way to begin

borisz · Joined: 16 Jun 2008 Posts: 1

Hello!

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Guest · Posted: Wed Jul 23, 2008 8:10 am

Hi

I got one LA1034 and one Poscope. Don't make compare to the product, because it's not possible.

The LA1034 is professionally tools but it cost more then Poscope.

I prefer the LA1034:-)

SherpaDoug · Joined: 07 Sep 2003 Posts: 1640 Location: Cape Cod Mass USA

The Poscope looked interesting until I ran into the 200kHz max digitizing frequency. Anything less than 50MHz is a non-starter for me. At 200kHz you can't even look at the clock of your PIC, or 115200 baud serial, even 100kHz SPI is going to be tough to decode.

I am happy with my LA1034, though I wish it had deeper memory.
_________________
The search for better is endless. Instead simply find very good and get the job done.