Merge pull request favalex#6 from RJ/write_single_register

Use function `0x6` for single register writes

README.rst

@@ -105,6 +105,9 @@ BINARY_TYPE = <pack format>
 VALUE = <number>
   The value to be written to the register. If not present, the register will be read instead.
 
+  If only one register is written to, the modbus function ``6 (0x6)``, "write single register" is used. 
+  If multiple registers are written to, the modbus function ``16 (0x10)``, "write multiple registers" is used.
+
 EXAMPLES
 ========
 

modbus_cli/access.py

@@ -180,7 +180,10 @@ def write_registers_send(self, modbus):
 
                 words.extend([h << 8 | l for h, l in grouper(struct.pack(pack_type, value), 2)])
 
-            message = modbus.protocol.write_multiple_registers(modbus.slave_id, self.address(), words)
+            if len(self.values_to_write) == 1:
+                message = modbus.protocol.write_single_register(modbus.slave_id, self.address(), words[0])
+            else:
+                message = modbus.protocol.write_multiple_registers(modbus.slave_id, self.address(), words)
 
         logging.debug('→ < %s >', dump(message))
 

modbus_cli/modbus_rtu.py

@@ -38,7 +38,7 @@ def receive(self, request):
             response += self.connection.read(1)
             count = 2 + response[-1]
             response += self.connection.read(count)
-        elif function in (5, 15):
+        elif function in (5, 6, 15):
             # Function with fixed size
             response += self.connection.read(6)
         elif function & 0x80: