Tcn75a i2c

ARandomOWl

New Member

• Aug 24, 2011

• #1

Hi Guys

I have a TCN75A temperature sensor interfaced to a PIC 18F2458. I am using C18 and it's software I2C library. I can successfully read the MSB of the temperature but the LSB always returns 255. Can anyone see anything wrong with my code?

Link to Pastbin

Thanks.

 

Ian Rogers

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• Aug 24, 2011

• #2

When you read / write I2C the Device sends the ack not you...

Here's My code

Code:

char ReadByte(int Address)
	{
	char Byte;
	SendID(0b10100000);
	if(SendByte(Address>>8)==0)
		return(0);
	if(SendByte(Address&0xff)==0)
		return(0);
	SendRestart();
	if(SendByte(0b10100001)==0)
		return(0);
	Byte=ReceiveByte();
	SendNack();
	SendStop();
	return(Byte);
	}

char SendByte(char Byte)
	{
	SSPBUF=Byte;
	WaitSSP();
	return(!SSPCON2bits.ACKSTAT);
	}

note... send byte returns the recived ack status

This code is for eeprom.... If you want my library you can try it..

 

Last edited: Aug 24, 2011

ARandomOWl

New Member

• Aug 24, 2011

• #3

Ian Rogers said:

When you read / write I2C the Device sends the ack not you...

Click to expand...

That's what I thought, but my code didn't work at all until I added those. How can I wait for an ACK using the SWI2C library?

 

Ian Rogers

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• Aug 24, 2011

• #4

Sorry I didn't think!! sw I2C Try this... https://www.microchipc.com/sourcecode/PIC_Hi-Tech_C_Mike_Pearces_I2C_routines.zip

 

ARandomOWl

New Member

• Aug 24, 2011

• #5

Thanks, I will look at the function in that code. There is an example in the C18 libraries PDF but I don't understand how it works.

This is it:

Code:

void ack_poll( void )
{
  SWStartI2C();
  var = SWPutcI2C( 0xA0 ); // control byte
  while( SWAckI2C() )
  {
    SWRestartI2C();
    var = SWPutcI2C(0xA0); // data
  }
  SWStopI2C();
}

 

Ian Rogers

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• Aug 25, 2011

• #6

Sorry! Hectic week... SwackI2C() does return the acknowledgement... So the code was correct... Have you tried to read just one byte and then the other in a new read?

Where about's in Manchester are you...

 

ARandomOWl

New Member

• Aug 25, 2011

• #7

Oh, ok. How would I go about doing that? The temperature register is 16 bits long and the pointer register only gives the option to point to that register and not a specific byte.

(Not far from Oldham )

 

Ian Rogers

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• Aug 25, 2011

• #8

Reading the data sheet... SEND START (wait for ack).... PUT ADDRESS (wait for ack )...PUT POINTER (wait for ack )...... SEND RESTART (wait for ack).....PUT ADDRESS (w.f.a.)....
READ MSB (YOU send ack).... READ LSB (YOU send ack ) ...... SEND STOP .....

You haven't got a send ack in software.. you'll have to make it... Have a look how Mike Pierce did it....

I live in Oldham....

C:

void i2csendack(void)
{
 //--- Send Ack to slave except for last time ---
 SDA=0;
 SDA_TRIS=I2CLOW;              //-- Send ACK
 i2cdelay(I2CDATASETTLE);      //-- Give it time to settle
 i2cclock();                   //-- Pulse the clock
 SDA_TRIS=I2CHIGH;             //-- Release ACK
 i2cdelay(I2CDATASETTLE);      //-- Gap between next byte
}
//************** END OF i2csendack

 

Last edited: Aug 25, 2011

ARandomOWl

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• Aug 25, 2011

• #9

Now I'm having a headache with Mike Pierce's code. Now all data received comes back as 0

 

ARandomOWl

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• Aug 25, 2011

• #10

Ignore the above post. I am back to the original code. I have added in the function in post 8 along with the corresponding "i2cclock" function and called i2csendack after I receive the first byte. I am still receiving 255 for the second byte.

 

Ian Rogers

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• Aug 25, 2011

• #11

Reason....All delays have to be set to your chip speed.. I ran it at 20mhz so I set all delays by increasing by 6 ie.. delay(10).. became delay(60)

 

ARandomOWl

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• Aug 25, 2011

• #12

I calculated the delays for my chip based on the defines in "m_i2c_1.c"

 

Ian Rogers

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• Aug 25, 2011

• #13

I'm just taking my daughter to the Leeds festival.... When I get back I'll try to simulate a multi-read.. Isis has the TC74 but not the 12 bit TCN75a.

 

ARandomOWl

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• Aug 26, 2011

• #14

Here is my new code, still not working. Link

 

Ian Rogers

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• Aug 26, 2011

• #15

Reading the data sheet... SEND START (wait for ack).... PUT ADDRESS (wait for ack )...PUT POINTER (wait for ack )...... SEND RESTART (wait for ack).....PUT ADDRESS (w.f.a.)....
READ MSB (YOU send ack).... READ LSB (YOU send ack ) ...... SEND STOP .....

Click to expand...

The read is still not complete... you have to put address then pointer.......RESTART then address then read msb... lsb

I didn't get home until really late last night I'll try and analyse tonight...

 

Ian Rogers

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• Aug 26, 2011

• #16

Right.... The SWgetsI2C(); function gets several bytes in succession.. It generates the required NACK for the transfer..

C:

 unsigned int read_Temp()
 {
     unsigned char data[2];

    SWStartI2C();
    SWWriteI2C(0x90);
    SWAckI2C();
    SWWriteI2C(0);
    SWAckI2C();
    SWRestartI2C();
    SWWriteI2C(0x91);
    SWAckI2C();
    SWGetsI2C(data,2);
    SWStopI2C(); 
    return(data[0] * 256 + data[1]); 
 }

It needs to be something like this

 

Last edited: Aug 26, 2011

ARandomOWl

New Member

• Aug 26, 2011

• #17

Why did I not even consider using that! Thanks! Now I have a meaningful LSB. Although it's only changing between 0 and 128 which maybe means I am not successfully putting it into 12bit mode?

 

ARandomOWl

New Member

• Aug 26, 2011

• #18

Ok, it turns out the config register isn't being set properly unless I call the TCN75A init routine twice.

 

Ian Rogers

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• Aug 26, 2011

• #19

Also.. That routine I posted.. You'll need to cast the return or the MSB may be lost..

 

ARandomOWl

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• Aug 28, 2011

• #20

Any idea why I have to call the init routine twice for it to work? It's the same even if I leave a large power on delay.