#255 Fix BinaryPayloadDecoder

Author: dhoomakethu

CHANGELOG.rst

@@ -4,6 +4,7 @@ Version 1.4.0
 * Check for slave unit id before processing the request for serial clients
 * Bug fix serial servers with Modbus Binary Framer
 * Bug fix header size for ModbusBinaryFramer
+* Bug fix payload decoder with endian Little
 * Support Database slave contexts (SqlStore and RedisStore)
 * Custom handlers could be passed to Modbus TCP servers
 * Asynchronous Server could now be stopped when running on a seperate thread (StopServer)

examples/common/modbus_payload.py

@@ -24,7 +24,7 @@ def run_binary_payload_ex():
     # ----------------------------------------------------------------------- #
     # We are going to use a simple client to send our requests
     # ----------------------------------------------------------------------- #
-    client = ModbusClient('127.0.0.1', port=5020)
+    client = ModbusClient('127.0.0.1', port=5440)
     client.connect()
 
     # ----------------------------------------------------------------------- #
@@ -41,7 +41,7 @@ def run_binary_payload_ex():
     # - an 8 bit int 0x12
     # - an 8 bit bitstring [0,1,0,1,1,0,1,0]
     # ----------------------------------------------------------------------- #
-    builder = BinaryPayloadBuilder(endian=Endian.Big)
+    builder = BinaryPayloadBuilder(endian=Endian.Little)
     builder.add_string('abcdefgh')
     builder.add_32bit_float(22.34)
     builder.add_16bit_uint(0x1234)
@@ -67,10 +67,10 @@ def run_binary_payload_ex():
     # - an 8 bit bitstring [0,1,0,1,1,0,1,0]
     # ----------------------------------------------------------------------- #
     address = 0x00
-    count = 8
+    count = len(payload)
     result = client.read_holding_registers(address, count,  unit=1)
     decoder = BinaryPayloadDecoder.fromRegisters(result.registers, 
-                                                 endian=Endian.Big)
+                                                 endian=Endian.Little)
     decoded = {
         'string': decoder.decode_string(8),
         'float': decoder.decode_32bit_float(),
@@ -84,7 +84,7 @@ def run_binary_payload_ex():
     print("Decoded Data")
     print("-" * 60)
     for name, value in iteritems(decoded):
-        print("%s\t" % name, value)
+        print("%s\t" % name, hex(value) if isinstance(value, int) else value)
 
     # ----------------------------------------------------------------------- #
     # close the client

pymodbus/payload.py

@@ -216,8 +216,8 @@ def fromRegisters(klass, registers, endian=Endian.Little):
         :param endian: The endianess of the payload
         :returns: An initialized PayloadDecoder
         '''
-        if isinstance(registers, list): # repack into flat binary
-            payload = b''.join(pack(endian + 'H', x) for x in registers)
+        if isinstance(registers, list):  # repack into flat binary
+            payload = b''.join(pack('!H', x) for x in registers)
             return klass(payload, endian)
         raise ParameterException('Invalid collection of registers supplied')