#!/usr/bin/python3

import serial

st="PMTK314,0,0,0,1,0,0,0,0,0,0,0,0,0,0"
EOL = "\r\n"
serial = serial.Serial("/dev/ttyAMA0", 38400)

i = 0
checksum = 0
while i < len(st):
   checksum ^= ord(st[i])
   i+= 1

data = bytes("$" + st + "*" + "%02X"%checksum + EOL, 'ascii')
serial.write(data)
print(data)