Adds the option to drop into zero mode for slaves

examples/common/asynchronous-server.py

@@ -72,6 +72,13 @@
 #         0x03: ModbusSlaveContext(...),
 #     }
 #     context = ModbusServerContext(slaves=slaves, single=False)
+#
+# The slave context can also be initialized in zero-mode which means that a
+# request to address(0-7) will map to the address (0-7). The default is
+# False which is based on section 4.4 of the specification, so address(0-7)
+# will map to (1-8)::
+#
+#     store = ModbusSlaveContext(..., zero-mode=True)
 #---------------------------------------------------------------------------# 
 store = ModbusSlaveContext(
     di = ModbusSequentialDataBlock(0, [17]*100),

examples/common/synchronous-server.py

@@ -72,6 +72,13 @@
 #         0x03: ModbusSlaveContext(...),
 #     }
 #     context = ModbusServerContext(slaves=slaves, single=False)
+#
+# The slave context can also be initialized in zero-mode which means that a
+# request to address(0-7) will map to the address (0-7). The default is
+# False which is based on section 4.4 of the specification, so address(0-7)
+# will map to (1-8)::
+#
+#     store = ModbusSlaveContext(..., zero-mode=True)
 #---------------------------------------------------------------------------# 
 store = ModbusSlaveContext(
     di = ModbusSequentialDataBlock(0, [17]*100),

pymodbus/constants.py

@@ -76,6 +76,11 @@ class Defaults(Singleton):
 
        The number of bits sent after each character in a message to
        indicate the end of the byte.  This defaults to 1.
+
+    .. attribute:: ZeroMode
+
+       Indicates if the slave datastore should use indexing at 0 or 1.
+       Mor about this can be read in section 4.4 of the modbus specification.
     '''
     Port          = 502
     Retries       = 3
@@ -89,6 +94,7 @@ class Defaults(Singleton):
     Parity        = 'N'
     Bytesize      = 8
     Stopbits      = 1
+    ZeroMode      = False
 
 
 class ModbusStatus(Singleton):

pymodbus/datastore/context.py

@@ -35,6 +35,7 @@ def __init__(self, *args, **kwargs):
         self.store['c'] = kwargs.get('co', ModbusSequentialDataBlock.create())
         self.store['i'] = kwargs.get('ir', ModbusSequentialDataBlock.create())
         self.store['h'] = kwargs.get('hr', ModbusSequentialDataBlock.create())
+        self.zero_mode  = kwargs.get('zero-mode', Defaults.ZeroMode)
 
     def __str__(self):
         ''' Returns a string representation of the context
@@ -56,7 +57,7 @@ def validate(self, fx, address, count=1):
         :param count: The number of values to test
         :returns: True if the request in within range, False otherwise
         '''
-        address = address + 1  # section 4.4 of specification
+        if not self.zero_mode: address = address + 1
         _logger.debug("validate[%d] %d:%d" % (fx, address, count))
         return self.store[self.decode(fx)].validate(address, count)
 
@@ -68,7 +69,7 @@ def getValues(self, fx, address, count=1):
         :param count: The number of values to retrieve
         :returns: The requested values from a:a+c
         '''
-        address = address + 1  # section 4.4 of specification
+        if not self.zero_mode: address = address + 1
         _logger.debug("getValues[%d] %d:%d" % (fx, address, count))
         return self.store[self.decode(fx)].getValues(address, count)
 
@@ -79,7 +80,7 @@ def setValues(self, fx, address, values):
         :param address: The starting address
         :param values: The new values to be set
         '''
-        address = address + 1  # section 4.4 of specification
+        if not self.zero_mode: address = address + 1
         _logger.debug("setValues[%d] %d:%d" % (fx, address, len(values)))
         self.store[self.decode(fx)].setValues(address, values)