User manual - METER PDU-4x0-W
11.
THE MODBUS PRO
TOCOL HANDLING
Transmission parameters: 1 start bit, 8 data bits, 1 or 2 stop bit (2 bits are send, 1 and 2 bits
are accepted when receive), no parity control
Baud rate:
selectable from: 1200 to 115200 bits/second
Transmission protocol:
MODBUS RTU compatible
The device parameters and display value are available via RS-485 interface, as HOLDING-
type registers (numeric values are given in U2 code) of Modbus RTU protocol. The registers
(or groups of the registers) can be read by 03h function, and wrote by 06h (single registers) or
10h (group of the registers) accordingly to Modbus RTU specification. Maximum group size for
03h and 10h functions can not exceeds 16 registers (for single frame).
The device interprets the broadcast messages, but then do not sends the answers.
11.1.
LIST OF REGISTERS
Register Write
Range
Register description
01h
No
-999 ÷ 9999 Measurement value (no decimal point)
02h
No
0h, A0h, 60h
The status of the current measurement;
0h
- data valid;
A0h
- top
border of the measurement range is exceeded;
60h
- bottom border
of the measurement range is exceeded;
03h
Yes
0 ÷ 3
“
Pnt
” parameter in “
InPt
” menu (decimal point position)
0
- “
0
”;
1
- “
0.0
”;
2
- “
0.00
”;
3
- “
0.000
”
04h
Yes
see descr.
State of the relays and alarm LED (binary format)
(1 - on, 0 - off):
00000000 000e00ba
a
- relay R1;
b
- relay R2;
e
- alarm LED;
If written, only
a
,
b
bits are important (others are ignored) these
bits allows user to control the relays via RS-485 interface
05h
1
Yes
0h ÷ 1800h
State of current output, expressed in 1/256 mA units – it means that
high byte express integer part, and low byte fractional part of
desired output current.
06h
No
-999 ÷ 9999 Peak (drop) value (no decimal point)
10h
Yes
0 ÷ 5
“
tyPE
” parameter in “
InPt
” menu (nominal input range).
0
- 0-20 mA range;
1
- 4-20 mA range;
2
- 0-10 V range;
3
- 2-10 V range;
4
- 0-5 V range;
5
- 1-5 V range
11h
Yes
0 ÷ 5
“
CHAr
” parameter in “
InPt
” menu (characteristic type)
0
- linear ;
1
- square;
2
- square root;
3
- user defined;
4
- volume
characteristics of a cylindrical tank in the vertical position;
5
-
volume characteristics of a cylindrical tank in the horizontal position
12h
Yes
0 ÷ 5
“
FiLt
” parameter in “
InPt
” menu (measurement filtering rate)
13h
Yes
0 ÷ 3
“
Pnt
”parameter in “
InPt
” menu (the copy of 03h register, decimal
point position)
0
- “
0
”;
1
- “
0.0
”;
2
- “
0.00
”;
3
- “
0.000
”
14h
Yes
-999 ÷ 9999 “
Lo C
” parameter in “
InPt
” menu, no decimal point included
15h
Yes
-999 ÷ 9999 “
Hi C
” parameter in “
InPt
” menu, no decimal point included
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