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Raspberry Pi fork of libmodbus with GPIO rx-tx functionality with RS485 chips or similar

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 (if the RE and DE are the same)
  • modbus_configure_rpi_bcm_pins : Configures GPIO BCM pins (RE & DE) to be used for rx-tx switching (if the RE and DE are not on the same pin)
  • 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 DE & RE used for switching
  • modbus_configure_rpi_bcm_pins(ctx,17,18); // configures BCM pin # 17 for DE and # 18 for RE used 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.