User manual - METER SRT-457
8.
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.
8.1.
LIST OF REGISTERS
Register
Write
Range
Register description
01h
No
-999 ÷ 6000
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
No
1
Decimal point position, constant value:
1
-
0.0
;
04h
Yes
see descr.
State of the relays and alarm LED (binary format)
(1 - on, 0 - off):
00000000 000edcba
a
- relay R1;
b
- relay R2;
c
- relay R3;
d
- relay R2;
e
- alarm LED;
If written, only
a
,
b
,
c
,
d
bits are important (others are ignored)
these bits allows user to control the relays via RS-485 interface
06h
No
-999 ÷ 6000 Peak (drop) value (no decimal point)
10h
Yes
0 ÷ 2
tyPE
parameter in
InPt
menu (input type).
0
- Pt-100;
1
- Pt-500;
2
- Pt-1000
12h
Yes
0 ÷ 5
FiLt
parameter in
InPt
menu (measurement filtering rate)
18h
Yes
-99 ÷ 99
toFS
parameter in
InPt
menu (shift of measurement scale),
expressed by 0,1°C
20h
2
Yes
0 ÷ 199
Device address
21h
No
21B2h
Device identification code (ID)
22h
3
Yes
0 ÷ 7
bAud
parameter in
rS
menu (baud rate);
0
- 1200 baud;
1
- 2400 baud;
2
- 4800 baud;
3
- 9600 baud;
4
- 19200 baud;
5
- 38400 baud;
6
- 57600 baud;
7
- 115200 baud
23h
4
Yes
0 ÷ 1
mbAc
parameter in
rS
menu (permission to write registers via
RS-485 interface);
0
- write denied ;
1
- write allowed
28
i