Collected informations for using Modbus on TCP/IP. Libmodbus is used as master on any Linux computer (Sheevaplug). Wago fieldbuscouplers 750-342 are used as slaves.

Source

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

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:

ipNumber= bootpEnabled ? getIpNumberFromBootpServer() : getIpNumberFromEeprom()

See also: Wago manual p.82ff and bootptab

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 here and 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.