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johnbravado
Joined: 07 Apr 2010
Posts: 11
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| General I2C questions PIC16F886 |
 Posted: Wed Apr 14, 2010 12:23 pm |
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I got 2 PIC16F886 communicating with each other. However, if I make the slave address odd, it doesn't work.
In the slave file I have
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#use i2c(slave, slow, force_hw, sda=PIN_C4, scl=PIN_C3, address=0x22);
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In the master
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#use i2c(master, slow, sda=PIN_C4, scl=PIN_C3)
#define SLAVE_ADDRESS 0x22
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This works fine, as done any even numbered address for the slave. As soon as I make the slave address odd, communication stops. Slave addresses 0x33, 0x31, 0x27 all fail to communicate. however 0x30, 0x24, 0x28 all succeed. I also tried to change the address of the slave device in the init function with i2c_slaveaddr(0x33) and it still failed to communicate. I need to be able to use 0x33.
Any ideas why I can't use odd numbers? |
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newguy
Joined: 24 Jun 2004
Posts: 1907
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| Posted: Wed Apr 14, 2010 12:29 pm |
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| The LSb is reserved as a read/write flag. I suspect this is the cause of your trouble. |
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PCM programmer
Joined: 06 Sep 2003
Posts: 21708
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| Posted: Wed Apr 14, 2010 12:40 pm |
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| Quote: | | I need to be able to use 0x33. |
Explain this. |
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johnbravado
Joined: 07 Apr 2010
Posts: 11
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| Posted: Wed Apr 14, 2010 12:53 pm |
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I am working in conjunction with another company. They have a product that wants to interact with ours through i2c communication. They already have many products out there in which their unit, DB, connect to other units, MB. The DB is the master, and it sends out i2c commands to the MB slave address 0x33. As such, we need to work with what they have. We cannot ask the company to use a different address, changing their code and many other peoples code, merely because the CCS compiler cannot handle odd number i2c slave address.
BTW i tested it and if you do the following from the master and change the slave address to 0x32, the slave sends a response. this makes no sense as to why the CCS compiler would eliminate the ability to use odd numbered address when all they had to do was put us in charge of the shifting and read/write bit at the end.
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i2c_start();
i2c_write(0x33);
response = i2c_read(0);
i2c_stop;
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PCM programmer
Joined: 06 Sep 2003
Posts: 21708
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johnbravado
Joined: 07 Apr 2010
Posts: 11
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| Posted: Wed Apr 14, 2010 1:48 pm |
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Thanks. I am thinking I am going to have to wait until I get their test box to fully explore this. Just for clarification of how this is working though.
If they are sending to slave address 0x33, I am going to have to address my unit as 0x66.
Just for further clarification. So when I am sending requests I got to think of it as a total byte not seven when it comes to the address. So lets say I was working with another company and they had addressed their units with slave address 0x2F. In order to write to them I would consider what I write for the address as the whole byte with the read/write appended, ie 0x5E for write and 0x5F for read? i2c_write(0x5E) or i2c_write(0x5F). |
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PCM programmer
Joined: 06 Sep 2003
Posts: 21708
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| Posted: Wed Apr 14, 2010 2:00 pm |
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For a Philips style slave address of 0x2F, the CCS-style equivalents are:
The i2c write address is 0x5E. The read address is 0x5F.
Look at this example. It has i2c Master and Slave code.
The slave address is 0x12. That address is entered into the #use i2c()
statement for the Slave. The Master then has two constants defined.
The write address is 0x12 and the read address is 0x13.
The two example programs in this post should show it clearly:
http://www.ccsinfo.com/forum/viewtopic.php?t=39242&start=6 |
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