Modbus TCP Client/Server

Based on libmodbus

• modbus-client is a standalone command line Modbus TCP client
• modbus-server is a Modbus TCP server that uses mysql to store register values

Usage

modbus-client ip_address slave_id r reg_type address [num_reg format]

modbus-client ip_address slave_id w reg_type address value [format]

Register Type

• 0 - Coil
• 1 - Discrete Input
• 3 - Input registers
• 4 - Holding registers

Format

• a - floating point abcd
• b - floating point badc
• c - floating point cdab
• d - floating point dcba
• (s)1 - 16-bit register. Optionally signed. Default.
• (s)3 - 32-bit register. Optionally signed.
• (s)6 - 64-bit register. Optionally signed.
• (s)k - 32-bit Mod10k. Optionally signed.
• (s)l - 48-bit Mod10k. Optionally signed.
• (s)m - 64-bit Mod10k. Optionally signed.

Install modbus-client

Install libmodbus

From libmodbus documentation:

chmod +x ./autogen.sh
./autogen.sh
./configure
make install

May need to do this depending on distribution

cp src/.libs/libmodbus.so* /usr/lib/
ln -s -f /usr/lib/libmodbus.so.5.1.0 /usr/lib/libmodbus.so.5
ln -s -f /usr/lib/libmodbus.so.5.1.0 /usr/lib/libmodbus.so

Compile modbus-client

gcc modbus-client.c -o modbus-client `pkg-config --libs --cflags libmodbus`

Install modbus-server

Install libmodbus (see above) and inih

Compile modbus-server

gcc inih/ini.c modbus-server.c -o modbus-server -std=gnu99 `mysql_config --cflags --libs` `pkg-config --libs --cflags libmodbus`
cp modbus-server /usr/bin/

Make sure mysql is installed with libmysqlclient-dev

Choose a database and create the following table

CREATE TABLE IF NOT EXISTS `modbusServer` (
    `id` int(11) NOT NULL AUTO_INCREMENT,
    `regType` int(11) NOT NULL,
    `address` int(11) NOT NULL,
    `val` int(11) NOT NULL DEFAULT '0',
    `modifiedCount` int(11) NOT NULL DEFAULT '0',
    `updated` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP,
    PRIMARY KEY (`id`),
    KEY (`regType`),
    KEY (`address`),
    UNIQUE KEY (`regType`, `address`)
) ENGINE=InnoDB;

Copy ini to /etc and fill in mysql information. Mysql user should have read/write access

cp modbus-server.ini /etc/

Run modbus-server

Optionally install modbus-server as a service

Install runit and execute the following commands

mkdir -p /etc/sv/modbus-server/log
mkdir /var/log/modbus-server
cat > /etc/sv/modbus-server/run <<- EOM
#!/bin/sh
exec /usr/bin/modbus-server 2>&1
EOM
cat > /etc/sv/modbus-server/log/run <<- EOM
#!/bin/sh
exec svlogd -tt /var/log/modbus-server/
EOM
chmod +x /etc/sv/modbus-server/run
chmod +x /etc/sv/modbus-server/log/run
ln -s /etc/sv/modbus-server /etc/service/