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...8 MODBUS FUNCTIONS
8.4 Preset Single Register – Function Code 06
8.4.1 Preset Single Register Query
The preset single register allows the user to modify the contents of a holding register.
Note. Function codes 5, 6 and 16 are the only messages that are recognized as valid for broadcast.
Example – a preset single register request to write the value 60.0 to holding register address 12 (alarm trip A1) in slave 01 is
shown below.
Since all register values for measured variables and alarm set points (scaled parameters) are ranged to 12 bits (for RTU), then
to calculate the Data Value High and Data Value Low for a setpoint of 60.0 the following method is used:
Instrument Range
therefore
converted to hexadecimal
therefore
Note. To write to a register, the register's offset address must be used, e.g. to write to register 12, the offset address
11(0B) is transmitted.
A
d
d
e r
s
s
F
u
n
t c
o i
n
0
1
0
6
8.4.2 Preset Single Register Response
The normal response to a preset single register request is to retransmit the query message after the register has been altered.
Example:
A
d
d
e r
s
s
F
u
n
t c
o i
n
0
1
0
6
10
=
0 to 100.0
60.0 x 4095
= 2457
100.0
2457
= 0999
10
Data Value High = 09
Data Value Low = 99
R
e
i g
t s
r e
R
e
i g
t s
r e
O
f
s f
t e
H
g i
h
O
f
s f
t e
L
o
0
0
0
B
R
e
i g
t s
r e
R
e
i g
t s
r e
O
f
s f
t e
H
g i
h
O
f
s f
t e
L
o
0
0
0
B
10
16
D
a
a t
V
a
u l
e
H
g i
h
D
a
a t
w
0
9
D
a
a t
V
a
u l
e
H
g i
h
D
a
a t
w
0
9
V
a
u l
e
L
o
w
E
r r
r o
C
h
e
c
k
F
9
9
3
E
V
a
u l
e
L
o
w
E
r r
r o
C
h
e
c
k
F
9
9
3
E
e i
d l
(
C
R
C
1 -
) 6
3
2
e i
d l
(
C
R
C
1 -
) 6
3
2
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