COM Port Objects

#Firmware/v310 #Serial

The COM port objects provide lower level control of the serial ports. This low level access is required for Modbus and SDI-12 communications (and can be used for other low-level serial control).

However, for this access, the COM port must not be used by a regular Collector Channel.

Acquire and Release

Once requested, the COM port object is acquired by the calling thread. Only the thread that has acquired the resource is allowed to access it.

If you need to pass over control to another thread, you need to call cpo:release(), and the other thread can then call cpo:acquire()... cpo:release()

e.g.

function AfterBootUp()
  modbus_port = serial.port(3)
  modbus_port:set('19200n8') -- set the protocol
  modbus.set(modbus_port)    -- enable RS485 mode
  modbus_port:release()      -- release so we can use this in another thread
end

function Modbus_Thread(the_thread, the_name)
  modbus_port:acquire()
  -- ... do work
  modbus_port:release()
end