:mod:`odbus` --- control slave modules on a PLC board
==========================================================

.. module:: odbus
   :synopsis: pyb.I2C wrapper to control slave modules on a PLC board

This module provides methods to list, read and write OD slave devices connected via I2C bus

class ODBUS
-------------

The ODBUS class provides a wrapper to I2C bus

Usage example::

    import odbus

    bus = odbus.ODBUS()
    odbus.list()
    bus.write(odbus.RELAY,odbus.CH1,1)  # Switch the relay on

Constructors
------------

.. class:: ODBUS()

    Construct an ODBUS object. The I2C bus is hard-coded. No additional parameters are required.

Query devices
--------------

.. method:: ODBUS.list()

    Query all devices currently on the bus.

.. method:: ODBUS.read(device, address)

    Read the value, currently stored in the *address* location of the EEPROM of the device with the address *device*. Predefined locations are:

    * *ID*   - the device ID
    * *ADDR* - the device address (i.e. *device*)
    * *RST*  - restart the device
    * *CH1*  - channel 1 (if present)
    * *CH2*  - channel 2 (if present)
    * *ALRM* - alarm condition

    Predefined device IDs:

    * ``RELAY`` - 0x08
    * ``IO``    - 0x09

.. method:: ODBUS.write(device, address, value)

    Write a value (must be an integer in the range of [0:255]) to the *address* location of the EEPROM of the device with the address *device*.

Constants
---------

.. data:: ID
          ADDR
          RST
          CH1
          CH2
          ALRM

   Predefined EEPROM locations.

.. data:: RELAY
          IO

   Predefined device IDs.