7 replies to this topic

[demonGeek]

I'm playing with I2C and a serial EEPROM (24LC32A) on my N+.

I have it working but I've run into a couple of issues that - I think - require more granular I2C control than I can get through the I2CDevice in Microsoft.SPOT.Hardware.

Here are a couple of examples from the 24LC32A datasheet:

• The datasheet describes an 'Acknowledge Polling Flow' which allows the code to loop while waiting for a write operation on the device to complete. You create a loop to send a control byte to the device and then parse the ACK looking for a zero at which point the device is ready to accept a new operation.
  
• The 'Random Read Sequence' which allows a byte to be read from a specified address requires a control sequence that includes a start signal (high to low transition on the SDA line while SCL is high) in the middle like this: START + CONTROL-BYTE + ADDR-HI + ADDR-LO + START + CONTROL-BYTE...STOP

Since the I2CDevice class seems to wrap everything up in an I2CTransaction, it seems that I don't have control over when the start signal gets sent or even the ability to parse the ACK.

Any thoughts/suggestions would be most welcome.

[CW2]

I'm playing with I2C and a serial EEPROM (24LC32A) on my N+.

• The 'Random Read Sequence' which allows a byte to be read from a specified address requires a control sequence that includes a start signal (high to low transition on the SDA line while SCL is high) in the middle like this: START + CONTROL-BYTE + ADDR-HI + ADDR-LO + START + CONTROL-BYTE...STOP

You'd need 4.1.1 alpha firmware for that (Repeated Start condition support).

[demonGeek]

You'd need 4.1.1 alpha firmware for that (Repeated Start condition support).

Thanks CW2, I have 4.1.1 firmware and the code from this post.

Please correct me if I'm wrong here but I don't think that's what I need. The repeated start condition fix seems to just be adding extra bytes immediately after the initial start signal. I don't see how that lets me generate this control sequence:

START + CONTROL-BYTE + ADDR-HI + ADDR-LO + START + CONTROL-BYTE...STOP

The problem is the (highlighted) start signal in the middle of the sequence - there's no preceding stop so I have to be able to generate a start signal in the middle of the control sequence (transaction). The relevant information from the datasheet is as follows:

To perform a random read operation, first the word address must be set. This is done by sending the word address to the 24LC32A as part of a write operation (R/W bit set to zero). After the word address is sent, the master generates a start condition following the acknowledge. This terminates the write operation, but not before the internal address pointer is set. Then the master issues the control byte again but with the R/W bit set to a one. The 24LC32A will then issue an acknowledge and transmit the 8-bit data word.

Here's the diagram from the datasheet:



I'm an experienced programmer but new to the whole electronics thing so I might have this all wrong - I just got my N+ and wanted to play with I2C; this EEPROM was the only I2C device I had lying around...

When I tested with the 4.1.1 firmware and revised I2C Transaction code I could see the extra bytes on the logic analyzer but I didn't see any extra start signals being generated.

[Chris Walker]

demonGeek, The "internalAddress" from the code you downloaded is the key here. Pass in the address [((0x100 * addressHigh) + addressLow), 2 bytes] as the internalAddress parameter and you should be good to go. Chris

[CW2]

The repeated start condition fix seems to just be adding extra bytes immediately after the initial start signal. I don't see how that lets me generate this control sequence:

START + CONTROL-BYTE + ADDR-HI + ADDR-LO + START + CONTROL-BYTE...STOP

The fix does exactly that (I know this for sure, because I have developed it and I have two working 24LCxx EEPROMs right in front of me ;- ). In order to generate the above sequence, call CreateReadTransaction(..., address, 2) from Chris' example. The address will be written onto the bus as ADDR-HI and ADDR-LO.

When I tested with the 4.1.1 firmware and revised I2C Transaction code I could see the extra bytes on the logic analyzer but I didn't see any extra start signals being generated.

Could you please share the logic analyzer output? (Please note that Start condition is just High -> Low transition on SDA while SCL is High, it is not a bit with duration of the clock signal period).

[demonGeek]

demonGeek,

The "internalAddress" from the code you downloaded is the key here. Pass in the address [((0x100 * addressHigh) + addressLow), 2 bytes] as the internalAddress parameter and you should be good to go.

Chris

Thanks Chris, that was the bit I was missing!

I totally misunderstood what that address was - I thought it was the device address.

It's working fine now.

[demonGeek]

The fix does exactly that (I know this for sure, because I have developed it and I have two working 24LCxx EEPROMs right in front of me ;- ). In order to generate the above sequence, call CreateReadTransaction(..., address, 2) from Chris' example. The address will be written onto the bus as ADDR-HI and ADDR-LO.


Could you please share the logic analyzer output? (Please note that Start condition is just High -> Low transition on SDA while SCL is High, it is not a bit with duration of the clock signal period).

Yeah, sorry CW2 - I misunderstood the internalAddress param on CreateReadTransaction (I thought it was the device address) so the extra Start wasn't getting generated. I fixed up the code and now it works perfectly - the logic analyzer output looks exactly like the datasheet.

Many thanks for your help - I still have a lot to learn but getting great help like this is always appreciated!

[demonGeek]

Having got this to work I thought it might be useful to post the test code I'm using so that others might benefit from it too:

public static void Main()
{
	byte[] buffer = new byte[1];
	int bytesWritten = 0;

	// Create the I2C device (device address: 0x54, clock rate: 50Khz)
	I2CDevice.Configuration i2cConfig = new I2CDevice.Configuration(0x54, 50);
	I2CDevice eeprom = new I2CDevice(i2cConfig);
			
	// Write the letter 'A' (0x41) to address 0x0000 on the eeprom
	I2CDevice.I2CTransaction[] writeTx = new I2CDevice.I2CTransaction[] { CreateWriteTransaction(new byte[] { 0x00, 0x00, 0x41 }, 0, 0) };
	bytesWritten = eeprom.Execute(writeTx, 1000);

	// Read the byte at address 0x0000 on the eeprom
	I2CDevice.I2CTransaction[]  readTx = new I2CDevice.I2CTransaction[] { CreateReadTransaction(buffer, 0x0000, 2) };
	do { bytesWritten = eeprom.Execute(readTx, 1000); } while (bytesWritten == 0);

	Debug.Print(buffer[0].ToString());

	Thread.Sleep(Timeout.Infinite);
}

#region see: http://forums.netduino.com/index.php?/topic/944-i2c-internaladdress-repeated-start-bit-support/

static I2CDevice.I2CWriteTransaction CreateWriteTransaction(byte[] buffer, uint internalAddress, byte internalAddressSize)
{
	I2CDevice.I2CWriteTransaction writeTransaction = I2CDevice.CreateWriteTransaction(buffer);
	Type writeTransactionType = typeof(I2CDevice.I2CWriteTransaction);

	FieldInfo fieldInfo = writeTransactionType.GetField("Custom_InternalAddress", BindingFlags.NonPublic | BindingFlags.Instance);
	fieldInfo.SetValue(writeTransaction, internalAddress);

	fieldInfo = writeTransactionType.GetField("Custom_InternalAddressSize", BindingFlags.NonPublic | BindingFlags.Instance);
	fieldInfo.SetValue(writeTransaction, internalAddressSize);

	return writeTransaction;
}

static I2CDevice.I2CReadTransaction CreateReadTransaction(byte[] buffer, uint internalAddress, byte internalAddressSize)
{
	I2CDevice.I2CReadTransaction readTransaction = I2CDevice.CreateReadTransaction(buffer);
	Type readTransactionType = typeof(I2CDevice.I2CReadTransaction);

	FieldInfo fieldInfo = readTransactionType.GetField("Custom_InternalAddress", BindingFlags.NonPublic | BindingFlags.Instance);
	fieldInfo.SetValue(readTransaction, internalAddress);

	fieldInfo = readTransactionType.GetField("Custom_InternalAddressSize", BindingFlags.NonPublic | BindingFlags.Instance);
	fieldInfo.SetValue(readTransaction, internalAddressSize);

	return readTransaction;
}

#endregion