.. _uss5-command-set:

Command Set
===========

Command IDs
-----------

The following table shows the available commands of the USBoard-USS5.


=============================== ===== ===========
Command                         Value Description
=============================== ===== ===========
``CMD_CONNECT``                 0     Check connection
``CMD_SET_CHANNEL_ACTIVE``      1     Activate channel for sending / receiving
``CMD_GET_DATA_1TO8``           2     Request data of sensors 1 to 8
``CMD_GET_DATA_9TO16``          3     Request data of sensors 9 to 16
``CMD_WRITE_PARASET``           4     Upload parameter set to board (volatile)
``CMD_WRITE_PARASET_TO_EEPROM`` 5     Write parameter set to board's EEPROM (non-volatile)
``CMD_READ_PARASET``            6     Read current parameter set
``CMD_GET_ANALOGIN``            7     Read values of analogue inputs
--                              8-12  Reserved
``CMD_GET_DATA``                13    Request data of all sensors
=============================== ===== ===========


CAN Communication
-----------------

The default base address is ``0x400``.
This base address can be changed in the parameter set.

The addresses used by the USBoard-USS5 are calculated from the base address by
adding the following offsets.

====================== ========
Offset to base address Function
====================== ========
``+0``                 Receive commands
``+1``                 Answer to ``CMD_CONNECT``
``+2``                 First answer to ``CMD_GET_DATA_1TO8``
``+3``                 Second answer to ``CMD_GET_DATA_1TO8``
``+4``                 First answer to ``CMD_GET_DATA_9TO16``
``+5``                 2nd answer to ``CMD_GET_DATA_9TO16``
``+6``                 Answer to ``CMD_READ_PARASET``
``+7``                 Answer to ``CMD_GET_ANALOGIN``
``+8``                 Answer to ``CMD_WRITE_PARASET``
``+9``                 Answer to ``CMD_WRITE_PARASET_TO_EEPROM``
``+13``                1st Answer to ``CMD_GET_DATA`` (group 0: 1 to 4)
``+14``                2nd Answer to ``CMD_GET_DATA`` (group 1: 5 to 8)
``+15``                3rd Answer to ``CMD_GET_DATA`` (group 2: 9 to 12)
``+16``                4th Answer to ``CMD_GET_DATA`` (group 3: 13 to 16)
====================== ========


USB / Serial Interface
----------------------


Communication via USB is done via a USB-serial-converter on the USBoard-USS5.
The computer's operating system can access it like a traditional serial interface.
On request the USB converter can be replaced by an RS-232 transmitter.
This does not affect the communication protocol of the serial interface.

.. note:: The RS-232 interface requires a common ground connection between the USBoard-USS5 and the computer.



The serial interface runs at 19200 Baud.
Its protocol has the same format as the CAN communication except for the following addition:

Every message **from** the USBoard-USS5 begins with a start byte which must have the value ``0xFF``.
After each message, made up of eight data bytes, a 16 bit checksum is sent.
Because of this, a complete message is 11 bytes long.

======== ========== ================== =================
Byte 1   Bytes 2-9  Byte 10            Byte 11
======== ========== ================== =================
``0xFF`` data bytes checksum high byte checksum low byte
======== ========== ================== =================

The checksum is calculated with an CRC-CCITT algorithm using 8 databytes.

Messages **to** the USBoard-USS5 only contain the data bytes.

Example implementation of the checksum calulation (C code):

.. literalinclude:: ../checksum.c
   :language: c