I2C
===

+--------+------------+---------------------+------------------+-------------+
| Pin    | Signal     | Description         | type             | I/O         |
+========+============+=====================+==================+=============+
| 40     | I2C_DATA   | I2C Data            | VDDIO            | I/O         |
+--------+------------+---------------------+------------------+-------------+
| 41     | I2C_CLK    | I2C Clock           | VDDIO            | O           |
+--------+------------+---------------------+------------------+-------------+
| **Module**          | **Devices connected to this I2C bus**                |
+---------------------+------------------------------------------------------+
| TX25, TX27, TX28S,  | No devices are connected to this I2C bus.            |
| TX51, TX53, TX6     | No pullup's are used on the module.                  |
+---------------------+----------+----------+------------------+-------------+
|                     | **Name** | **Type** | **Speed [kbps]** | **Address** |
+---------------------+----------+----------+------------------+-------------+
| TX28                | DS1339   | RTC      | 400              | 1101000 r/w |
+                     +----------+----------+------------------+-------------+
|                     | PCA9554  | IO       | 400              | 0100000 r/w |
+---------------------+----------+----------+------------------+-------------+
| TX48                | DS1339   | RTC      | 400              | 1101000 r/w |
+                     +----------+----------+------------------+-------------+
|                     | LTC3589  | PMIC     | 400              | 0110100 r/w |
+---------------------+----------+----------+------------------+-------------+

The I2C is a two-wire, bidirectional serial bus that provides a simple, efficient method of data exchange, minimizing the interconnection between devices. This bus is suitable for applications requiring occasional communications over a short distance between many devices. The flexible I2C allows additional devices to be connected to the bus for expansion and system development.

.. figure:: ../images/i2c.png
   :align: center

Example I2C Voltage Level Translator (TX27 and TX51 only)
----------------------------------------------------------

The Texas Instruments PCA9306 allows bidirectional voltage translations between 1.2V and 5V, without the use of a direction pin.

**Be aware of the PCA9306 min. supply voltage: VREF2 > VREF1 + 0.6V. Because of this limitation a Texas Instruments TXS0102 should be used instead if the design is intended to be used with 1.8V and 3.3V TX modules.**

As with the standard I2C system, pullup resistors are required to provide the logic high levels on the translator's bus. The PCA9306 has a standard open-collector configuration of the I2C bus. The size of these pullup resistors depends on the system, but each side of the repeater must have a pullup resistor. The device is designed to work with standard-mode and fast-mode I2C devices, in addition to SMBus devices. Standard-mode I2C devices only specify 3 mA in a generic I2C system where standard-mode devices and multiple masters are possible. Under certain conditions, high termination currents can be used.

.. figure:: ../images/example_i2c.png
   :align: center

.. figure:: ../images/tabelle_example_i2c.png
   :align: center

I2C recommendations [2]_
-------------------------

+---------------------------------------------------------------------+-----------------------------------------------------------------------+
| Recommendation                                                      | Explanation                                                           |
+=====================================================================+=======================================================================+
| Verify the target I2C interface clock rates.                        | The bus can only operate as fast as the slowest peripheral on the     |
|                                                                     | bus. If faster operation is required, move the slow devices to        |
|                                                                     | another I2C port. A slow peripheral may unpredictably take over the   |
|                                                                     | bus or might malfunction in some other way.                           |
+---------------------------------------------------------------------+-----------------------------------------------------------------------+
| Verify that the target I2C address range is supported and does no   | If it is undesirable to move a conflicting device to another I2C      |
| conflict with other peripherals. If there is an unavoidable address | port, review the peripheral operation to see if it supports remapping |
| conflict, move the offending device to another I2C port.            | the address.                                                          |
+---------------------------------------------------------------------+-----------------------------------------------------------------------+
| Do not place more than one set of pullup resistors on the I2C lines | This can result in excessive loading. Good design practice is to      |
|                                                                     | place one pair of pullups only.                                       |
+---------------------------------------------------------------------+-----------------------------------------------------------------------+

.. [2] Freescale Hardware Development Guide for i.MX 6Quad, 6Dual, 6DualLite, 6Solo Families of Applications Processors, Table 1-4