I2C Read/Write problems

[JD123]

Any suggestions on how to get the correct device address sent ($10), and read the address $22?

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

$10 = %00010000

PBP handles the R/W bit (bit.0), so your sending out address %0001000R (Read or Write bit) and the address "seen" by the receiving device is %00001000

Remember that I2C device addresses are shifted left one place to allow for the read/write bit. You'll never (edit: never say never - there are 10 bit addressing in some devices, though this is not part of the original I2C design data) see an I2C device address over $7F, or %01111111 or DEC127.

So, I think you should be using the DEVICE ADDRESS of $20

[mister_e]

Doesn't sounds right to me... how about most I2C EEPROM with $A0?

[JD123]

Doesn't sounds right to me... how about most I2C EEPROM with $A0?

Sorry, I overlooked your post. Are you seeing what I'm saying?

[mister_e]

Not sure... sure i misunderstand what you said.

        addr var word
        CTL CON $A0
        addr=$F0F0

SendIt:
        I2CWRITE PORTD.6, PORTD.7,CTL,addr,[$F1F2]
        pause 50
        goto sendit

will looks like...
<img src="http://www.picbasic.co.uk/forum/attachment.php?attachmentid=2461&stc=1&d=120717761 2">

But yeah.. on some device, the Address can be mixed with the ControlByte. EEPROMs such as some 24C04, c08 and c16 work like that.
<img src="http://www.picbasic.co.uk/forum/attachment.php?attachmentid=2462&stc=1&d=120717799 9">

They call it page select (sort of)... those Px bits...

NOTE: well it's not a 24lc64screenshot but anyways.

[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.

[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.