def __init__ (self, packet_str):
self.packet = array.array('B')
self.packet.fromstring(packet_str)
self.station = self.packet[0]
self.function = self.packet[1]
self.register = self.packet[3] + (self.packet[2]<<8)
self.data = self.packet[5] + (self.packet[4]<<8)
if self.packet[4] & 0x80: #its negative, perform 2's complement'
self.data = -(~self.data + (2<<15))
self.CRC = self.packet[6] + (self.packet[7]<<8)
payload = struct.pack('BBBBBB',
self.packet[0],
self.packet[1],
self.packet[2],
self.packet[3],
self.packet[4],
self.packet[5])
self.calculated_CRC = crc16(payload)
def buildpacket(self):
self.packet[0] = self.station = PC_STATION
self.packet[1] = self.function
if self.function == FUNCTION_READ_INPUT_REGISTER:
self.packet[2] = 1
self.packet[3] = self.data >> 8
self.packet[4] = self.data & 0x00FF
payload = struct.pack('BBBBB',
self.packet[0],
self.packet[1],
self.packet[2],
self.packet[3],
self.packet[4])
if self.function == FUNCTION_WRITE_SINGLE_REGISTER:
self.packet[2] = self.register >> 8
self.packet[3] = self.register & 0x00FF
# self.packet[4] = self.data >> 8
self.packet[5] = self.data & 0x00FF
payload = struct.pack('BBBBBB',
self.packet[0],
self.packet[1],
self.packet[2],
self.packet[3],
self.packet[4],
self.packet[5])
self.CRC = crc16(payload)
if self.function == FUNCTION_READ_INPUT_REGISTER:
self.packet[6] = self.CRC >> 8
self.packet[5] = self.CRC & 0x00FF
if self.function == FUNCTION_WRITE_SINGLE_REGISTER:
self.packet[7] = self.CRC >> 8
self.packet[6] = self.CRC & 0x00FF
