I2C Read/Write problems

[skimask]

If the device address is $10 then doesn't the address have to be left shifted one place?

I thought PBP handled that part for you. 'cause with a generic serial eeprom, the address is something like $a0, and that's how you address it...$a0, without the left shift, PBP handles the R/W bit.
But then again, we don't know exactly what kind of secret magic device is being addressed here...

[JD123]

I thought PBP handled that part for you. 'cause with a generic serial eeprom, the address is something like $a0, and that's how you address it...$a0, without the left shift, PBP handles the R/W bit.
But then again, we don't know exactly what kind of secret magic device is being addressed here...

$A0 is the LOWER 7 bit's of the address, shifted left one place. The DEVICE address being sent out and 'seen' by the reciever is %01010000, or $50. Check the specs of I2C, not just EEPROMS. The device address is specified as a 7 bit address, not 8. But since we are adding the R/W bit to the 8 bit address byte, we have to left shift the DEVICE address one place.

The confusion comes in dealing with 2 different data "specs" or "types" combined into one 8 bit Byte being send. Then suming the two values to "use" one value. That "one" value is not the device address.

You ever do this: (I know I have)
Gang 8 64KBit EEproms and use the device address (bit 4:1) by just rolling the long address over directly into the device address. It won't work. Trust me, just shift the address left once to embed the address into the device address byte.

[skimask]

The DEVICE address being sent out and 'seen' by the reciever is %01010000, or $50. Check the specs of I2C, not just EEPROMS. The device address is specified as a 7 bit address, not 8. But since we are adding the R/W bit to the 8 bit address byte, we have to left shift the DEVICE address one place........

I guess that's what I'm saying here...is that PBP handles it for us.

The confusion comes in dealing with 2 different data "specs" or "types" combined into one 8 bit Byte being send.

Confusion say...Man who live in glass house...should dress in basement...

[JD123]

Confusion say...Man who live in glass house...should dress in basement...

My spell checker wants another quarter and I'm too cheap to give it up!

[JD123]

I guess that's what I'm saying here...is that PBP handles it for us.

No. it doesn't. PBP handles the R/W bit for us. We still have to give it the correct address, formated to the device address byte. That's why you send %10100000 and the reciever "sees" %01010000 as the device address.

Now, if the receiving device specs say "send $xyz" then they have already formated the address for you. That still doesn't change the fact that the address is the upper 7 bits shifted right one place.

[skimask]

No. it doesn't. PBP handles the R/W bit for us. We still have to give it the correct address, formated to the device address byte. That's why you send %10100000 and the reciever "sees" %01010000 as the device address.

Ok, I'm smelling what your cooking... I'm pickin' up what you're layin' down...
(what happens if we overclock that same PIC to 50Ghz to get really fast I2C? )

[Dispersion123]

Wow... lots of help... I'm attempting to get the read to work, using $20 for the control byte. I'll see what I can do... eventually I want to be able to read and write registers using the LCD screen as sort of a 'menu' guide, and using my last to ports as button inputs.

EDIT:

Can anyone give me an idea as to why the clock is so far off? The book says 400KHz devices are accessible if the clock is above 8MHz (I'm using 20), but my clock is at 122Khz. The manufacturer of the board said this wasn't a problem so long as the PIC supported 'clock stretching'.

If anyone is interested, what I'm trying to connect to is an 'Open Servo' board.

[skimask]

Can anyone give me an idea as to why the clock is so far off? The book says 400KHz devices are accessible if the clock is above 8MHz (I'm using 20), but my clock is at 122Khz. The manufacturer of the board said this wasn't a problem so long as the PIC supported 'clock stretching'.

See Post #2...
400Khz is the MAXIMUM for most fast I2C devices. It's not neccessarily the speed that the PIC is communicating to said I2C device. I2CRead/I2CWrite are software, 'bit-banged' commands, not hardware.
If you ran your PIC clock at 40Mhz vs. 20Mhz, the I2C clock may very well jump up to 244Khz.

[JD123]

Wow... lots of help... I'm attempting to get the read to work, using $20 for the control byte. I'll see what I can do...

Here's the $24 million dollar question:

Does the documents for the slave IC say send address $10 or does it say that its address is $10.

So far as the clocking speed, there can be pulses that come close to 400k being send out, but that's just for a short period of time. The clocking speed will most likely vary in speed depending on what's being done. BTW, how are you reading the clocking speed? O-scope or frequency counter?

[JD123]

Ok, I'm smelling what your cooking... I'm pickin' up what you're layin' down...
(what happens if we overclock that same PIC to 50Ghz to get really fast I2C? )

50Ghz? Don't know, but I think you can use the IC as a hot-plate to keep your coffee warm.