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GFK-1541B Chapter 4 Programming Modbus/TCP Channel Commands 4-7
4
COMMREQ Status Word:
The Ethernet Interface updates the CRS word to show success or
failure of the command. Command words 3 and 4 specify the PLC memory location of the CRS
word.
(Word 3) COMMREQ Status Word Memory Type:
This word specifies the memory type for the
CRS word. The memory types are listed in the table below:
Type Value
(Decimal)
Value
(Hex.)
Description
%R 8 08H Register memory (word mode)
%AI 10 0AH Analog input memory (word mode)
%AQ 12 0
CH
Analog output memory (word mode)
%I 16
70
10H
46H
Discrete input memory (byte mode)
Discrete input memory (bit mode)
%Q 18
72
12H
48H
Discrete output memory (byte mode)
Discrete output memory (bit mode)
%T 20
74
14H
4AH
Discrete temporary memory (byte mode)
Discrete temporary memory (bit mode)
%M 22
76
16H
4CH
Discrete momentary internal memory (byte mode)
Discrete momentary internal memory (bit mode)
%G 56
86
38H
56H
Discrete global data table (byte mode)
Discrete global data table (bit mode)
(Word 4) COMMREQ Status Word Address Offset:
This word contains the offset within the
memory type selected.
The status word address offset is a zero-based number.
For example, if
you want %R1 as the location of the CRS word, you must specify a zero for the offset. The offset
for %R100 would be 99 decimal. Note, however, that this is the only zero-based field in the
Channel commands.
(Word 5):
Reserved. Set to zero.
(Word 6):
Reserved. Set to zero.
(Words 7 and up) Data Block:
The Data Block defines the Channel command to be performed.
For information on how to fill in the Channel command information, see the next section.