Serial port communication in LM2

Source code

port, err = serial.open(device, params)

Parameters:

• device port device name, required
• params parameters table, optional, (defaults are in bold):
  • baudrate 300, 600, 1200, 2400, 4800, 9600, 19200, 38400, 57600, 115200, 230400
  • parity “none”, “even”, “odd”
  • databits 5, 6, 7, 8
  • stopbits 1, 2
  • duplex “full”, “half” (Note: “half” is required for RS-485)

Reads the specified number of bytes, execution is blocked until read is complete

Source code

res, err = port:read(bytes)

Parameters:

• bytes number of bytes to read

 

Reads until timeout occurs or the specified number of bytes is received, whichever happens first.
Returns data plus number of bytes read, or, in case of error, nil plus error message

Source code

res, err = port:read(bytes, timeout)

Parameters:

• bytes number of bytes to read
• timeout maximum time to wait for read to complete, minimum value and timer resolution is 0.1 seconds

 

Flushes any read/unsent bytes

Source code

port:flush()

 

Closes serial port, no other port functions may be called afterwards

Source code

port:close()

 

Example (resident scripts, RS-485 echo test)

Source code

-- open port on first call
if not port then
require('serial')
port = serial.open('/dev/ttyS2', { baudrate = 9600, parity = 'even', duplex = 'half' })
port:flush()
end
 
-- port ready
if port then
-- read one byte
char = port:read(1, 1)
-- send back if read succeeded
if char then
port:write(char)
end
end