Siemens SIMATIC S7 - Page 474

Libraries
9.2 Overview of Modbus communication
S7-200 SMART
474 System Manual, V2.3, 07/2017, A5E03822230-AF
Mapping Modbus addresses to CPU addresses
All Modbus addresses are one-based.
Table 9- 1 Mapping Modbus addresses to CPU addresses
Modbus address
CPU address
00001
Q0.0
00002 Q0.1
00003
Q0.2
...
...
00255
Q31.6
00256
Q31.7
10001
I0.0
10002
I0.1
10003
I0.2
...
...
10255
I31.6
10256
I31.7
30001
AIW0
30002
AIW2
30003
AIW4
...
...
30056
AIW110
40001
400001
Vx (Holding reg. start)
40002
400002
Vx+2 =(Hold reg. start+2)
40003
400003
Vx+4 =(Hold reg. start+4)
... ...
4yyyy
4zzzzz
Vx+2(yyyy-1) or Vx+2(zzzzz-1)
MBUS_INIT parameters that limit slave accessibility
The Modbus slave/protocol allows you to limit the number of inputs, outputs, analog inputs,
and holding registers (V memory) that are accessible to a Modbus master.
●
MaxIQ
assigns the maximum number of discrete inputs or outputs (Is or Qs) a Modbus
master is allowed to access.
●
MaxAI
assigns the maximum number of input registers (AIWs) a Modbus master is
allowed to access.
●
MaxHold
assigns the maximum number of holding registers (V memory words) a Modbus
master is allowed to access.
See the description of the MBUS_INIT (Page 491) instruction for more information on setting
up the memory restrictions for the Modbus slave.