I2C issue

[Charles Linquis]

I'm trying to use the uChip MCP4561 EEPOT. I can read from it just fine, I just can't do a write using I2CWRITE, and Microchip tells me that the device must have a NACK at the end of each data transfer in order to work properly.

For example:

If I want to WRITE two bytes tp address 0x5D, I use the code

I2CAddress = $5D

I2CWRITE SDA,SCL,I2CAddress, Command,[Byte1,Byte2]

PBP sends out the WRITE request to the Address and gives an ACK
It sends out the command and gives an ACK
It sends byte 1 and gives an ACK
It sends byte 2 and gives an ACK <- should give NACK here, since this is the last byte of the transfer.

The MCP4561 holds the data bus low (forever). Is this a fault in PBP or my logic? In any case, does anyone know what I should try next?

[mackrackit]

Darrel can probably tell you how to mod a lib.
In the mean time maybe SHIFTOUT will work?
http://www.picbasic.co.uk/forum/cont...-EEPROM-Part-1

[Charles Linquis]

Thanks for the link, I may have to use that technique. I'm currently setting up the hardware to do the WRITE.
I already use it for READ.
I have never been 100% successful in getting the HW WRITE to work, so I usually just fall back to bit
banging. Fortunately, I'm hooked up to the real SDA and SCL on the chips.
It was always real easy to do a master-slave thing by sending in software and receiving in hardware,
you don't have to reconfigure any registers.

And for those of you that want to play with I2C: If you use my interrupt-driven slave (posted on this forum), you can
use I2CREAD and I2CWRITE at the same time the slave is running. One chip at both ends of the conversation!
A great debugging tool.

[Charles Linquis]

The SHIFTOUT / SHIFTIN method does, indeed look like it is going to work. I get a lot more control over what is going on.
I don't have eveything configured perfectly yet, but Thanks!

[mackrackit]

Cool!!!

[Charles Linquis]

BUT --- I can't use the shiftin/shiftout commands to write I2C. It violates the open-collector spec. That leaves me with a couple of options:
1. Learn to use the hardware
2. Modify the library to give shiftin/shiftout an open-collector mode (like I already have with DEBUG)
3. Do everything at the bit level myself.