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====== Modbus TCP ==

Collected informations for using [[wp>Modbus]] on TCP/IP. Libmodbus is used as master on any Linux computer ([[Sheevaplug]]). Wago fieldbuscouplers [[http://www.wago.com/wagoweb/documentation/750/ger_manu/342/m034200d.pdf|750-342]] (or alternatively [[http://www.wago.com/wagoweb/documentation/750/ger_manu/841/m084100d.pdf|750-841]]) are used as slaves.

===== Modbus Command Overview ==

^ Code ^ Target ^ Count ^ Direction ^  Name in Spec             ^ Libmodbus 3 fkt name                ^  libmodbus 2 fkt name         ^
|  ''01 0x01'' |  DO   |  many  |  read     | Read Coils                | ''modbus_read_bits''                | ''read_coil_status''          |
|  ''02 0x02'' |  DI   |  many  |  read     | Read Discrete Inputs      | ''modbus_read_input_bits''          | ''read_input_status''         |
|  ''03 0x03'' |  AO   |  many  |  read     | Read Holding Registers    | ''modbus_read_registers''           | ''read_holding_registers''    |
|  ''04 0x04'' |  AI   |  many  |  read     | Read Input Register       | ''modbus_read_input_registers''     | ''read_input_registers''      |
|  ''05 0x05'' |  DO   |  one   |  write    | Write Single Coil         | ''modbus_write_bit''                | ''force_single_coil''         |
|  ''06 0x06'' |  AO   |  one   |  write    | Write Single Register     | ''modbus_write_register''           | ''preset_single_register''    |
|  ''15 0x0f'' |  DO   |  many  |  write    | Write Multiple Coils      | ''modbus_write_bits''               | ''force_multiple_coils''      |
|  ''16 0x10'' |  AO   |  many  |  write    | Write Multiple registers  | ''modbus_write_registers''          | ''preset_multiple_registers'' |
|  ''23 0x17'' | AI/AO |  many  |  both     | Wrt/Rd Multiple registers | ''modbus_write_and_read_registers'' |  :?:  |

Sources [[http://www.modbus.org/docs/Modbus_Application_Protocol_V1_1b.pdf|Spec]] [[http://libmodbus.org/site_media/html/libmodbus.html|Manpage]]

More information sources:
  * http://www.anybus.de/technologie/modbustcp.shtml
  * http://www.modbus.org/docs/PI_MBUS_300.pdf
  * http://jamod.sourceforge.net/kb/protocol.html

===== Wago 750-342 ==
==== Setting the IP with bootp ==

Basic principle: The bootp client (750-342) sends its MAC address to the bootp server (eg. a slackware linux computer). The server in turn provides the client with an IP address.

Example: To provide the client host with the name ''etb-130'' who has the MAC address ''0030DE010A2C'' with the IP address ''192.168.132.130'' and an appropriate subnet mask, add the following line to ''/etc/bootptab'':

  etb-130:ht=1:ha=0030DE010A2C:ip=192.168.132.130:sm=255.255.255.0

Then, on the server machine, start the bootp daemon by uncommenting the following line in ''/etc/inetd.conf''

  bootps  dgram   udp     wait    root    /usr/sbin/bootpd        bootpd

...and restart the inetd:

  /etc/rc.d/rc.inetd restart

Now connect the Client with the server eg over crosslink cable and boot the client.

The 750-342 fetches its IP from the bootp server only when bootp is enabled. Otherwise it uses the IP saved in its EEPROM. Pseudcode:

<code c>
ipNumber= bootpEnabled ? getIpNumberFromBootpServer() : getIpNumberFromEeprom()
</code>

Web access to 750-342 is ''admin / wago''

See also: [[http://www.wago.com/wagoweb/documentation/750/ger_manu/841/m084100d.pdf|Wago manual]] p.82ff and [[man>bootptab]]

===== Libmodbus ==
==== Usage / Doc  ==

See http://libmodbus.org/site_media/html/libmodbus.html

==== Installation ==

Download the [[http://github.com/downloads/stephane/libmodbus/libmodbus-3.0.2.tar.gz|source]] and use the [[http://think-deep.com/becki/slackbuilds/pack.php?n=libmodbus|Slack build script]].

<note warning>The rest of this section is obsolete</note>

Note: You could get the latest devel release with ''git clone http://github.com/stephane/libmodbus.git'', but this has no ''configure'' script, so we use the lataest stable release instead.

Download v 2.0.3 from [[http://libmodbus.org/download/|here]]

Libmodbus has the unpleasant behaviour, that it prints error messages to ''stdout'' instead of ''stderr''. If you plan to build your application like a filter which commuicates over ''stdin / stdout'' to the world, than you will get problems, in that libmodbus may interfere your protocoll or whatever with error messages. Therfore we patch the source a little bit and are writing error messages to ''stderr'' instead of ''stdout''. Look for the function ''error_treat'' in ''modbus/modbus.c'' and replace the ''printf'' function with ''fprintf'':

<code c>
static void error_treat(modbus_param_t *mb_param, int code, const char *string)
{
        printf("\nERROR %s (%d)\n", string, code);
</code>

<code c>
static void error_treat(modbus_param_t *mb_param, int code, const char *string)
{
        fprintf(stderr, "\nERROR %s (%d)\n", string, code);
</code>

Now do the usual ''./confiure; make; su; make install;''. This installs the following objects to ''/usr/local/'':

  lib/libmodbus.so
  lib/libmodbus.la
  lib/libmodbus.so.2.0.0
  lib/pkgconfig/modbus.pc
  lib/libmodbus.so.2
  include/modbus/modbus.h

Then do ''ldconfig'' to update the library system info.


===== Wago Adressing in Libmodbus ==
==== Bit-based access to digital IOs ==

  * Bit-based function codes are # 1,2,5,15
  * The first digital input and output bits have both address 0
  * The 2nd digital input and output bits have both address 1
  * Addressing of inputs and outputs are independent (ie. there exists DI 0 and DO 0)
  * Each input/output bit consumes one member of the ''uint8_t dest[]'' array. I.e. each bit consumes one byte.

==== Register-based access to analog IOs ==

  * Register-based (16bit) function codes are # 3,4,6,16
  * The first analog input and output register have both address 0
  * Contrary to the Wago manuals the 2nd analog input and output registers have address 1 :!:

==== Register-based access to digital IOs ==

  * Access to digital inputs and outputs is also possible with the register-based function codes
  * Digital input and output addresses are automatically appended after the analog addresses. This means the digital addresses are dependend of the number of the analog devices.
  * Each digital IO consumes on //bit// in the ''uint16_t dest[]'' array
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