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Modbus/USS
3.6 Modbus Slave Driver
"From/To" Modbus address
The "From" address can be used to parameterize the Modbus address at the start of the
relevant area (e.g., flags, outputs, etc.). In other words, it is the first bit number in the area.
The "To" address can be used to parameterize the Modbus address at the end of the
relevant area (e.g., flags, outputs, etc.). In other words, it is the last bit number in the area.
The "From"/"To" addresses refer to the Modbus address in the transmission message frame
(bit numbers as of 0) for function codes FC 01, 05 and 15.
The individual "From/To" areas must not overlap.
Gaps between the individual "From/To" areas are permitted.
SIMATIC "As of" memory area
"As of" can be used to specify the start of the SIMATIC area to which the "From/To" Modbus
area is mapped (= first flag byte/output byte/timer/counter number of the SIMATIC area).
Example for FC 01, 05, 15
Table 3- 35
Converting Modbus addressing for function codes FC 01, 05, 15
Parameter DB
Input
Significance
From 0
From 0 to 65,535 (decimal)
Starting with this Modbus
address
Up to 2,047
From 0 to 65,535 (decimal)
Including this Modbus
address
SIMATIC memory area
As of
From 0 to 65,535 (decimal)
As of this flag byte
Flag
F 1000.0
SIMATIC flags area
Modbus address in
transmission message frame
(bit number)
(flag)
SIMATIC outputs area
Modbus address in
From 2,048
From 0 to 65,535 (decimal)
Starting with this Modbus
address
(bit number)
Up to 2,559
From 0 to 65,535 (decimal)
Including this Modbus
address
SIMATIC memory area
As of
From 0 to 65,535 (decimal)
As of this output byte
Outputs
Q 256.0
transmission message frame
(output byte number)
SIMATIC timers area
Modbus address in
From 4,096
From 0 to 65,535 (decimal)
Starting with this Modbus
address
(bit number)
Up to 4,255
From 0 to 65,535 (decimal)
Including this Modbus
address
SIMATIC timers memory area
As of
From 0 to 65,535 (decimal)
(timer number)
T 100
As of this timer (= 16-bit
word)
transmission message frame
Serial interface modules
Operating Instructions, 03/2009, A5E00124881-05
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