lukasz-skalski / libmodbus

A Modbus library for Linux, Mac OS X, FreeBSD, QNX and Windows

This is the Raspberry Pi fork of libmodbus () with GPIO rx-tx functionality RS485 chips

When it should be used :

If you're using an UART to RS485 conversion chip like 75176 or anything similar and using one of the RPi GPIO to switch rx - tx functionality of the chip.

In addition to standard libmodbus API, addtional APIs are included to support GPIO based rx-tx switching

Additional APIs :

modbus_enable_rpi : Sets an enable Rpi integer in ctx data structure.

modbus_configure_rpi_bcm_pin : Configures GPIO BCM pin to be used for rx-tx switching

modbus_rpi_pin_export_direction : export configured GPIO, configures it as an output.

modbus_rpi_pin_unexport_direction : unexport configured GPIO, configures it as an input.

Usage :

While initializing :

modbus_enable_rpi(ctx);

modbus_configure_rpi_bcm_pin(ctx,18); // configures BCM pin # 18 for switching

modbus_rpi_pin_export_direction(ctx); // exports configured BCM pin #

While clean up :

modbus_rpi_pin_unexport_direction(ctx); //unexport configured BCM pin #

Examples

See test.c in rpi-test folder for template.