User manual - RATEMETER STI-73
10.
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.
10.1.
LIST OF REGISTERS
Some parameters are located on two registers (higher word in first register, and lower word in
next one). After writing of one of them device controls result of their 32-bit value, and if it is
necessary corrects value of second register automatically. If appropriate modification is
impossible, both registers stay unaffected and device responds with error code 03h
(see:
TRANSMISSION ERRORS DESCRIPTION
).
Register Write
Range
Register description
01h
1
02h
1
No
0 ÷ 999999 Measurement value (no decimal point)
03h
No
0-FFh
The status of the current measurement.
0
– data valid;
20h
– device waits for first pulse;
A0h
– alarm state, allowable frequency range is exceeded
04h
Yes
0 ÷ 5
“PrEc”
parameter in
“inPUt”
menu. The same as 12h register
05h
Yes
0 ÷ 31
State of the relays and alarm LED (binary format)
(1 - on, 0 - off):
00000000 000e000a
a
- relay R;
e
- alarm state indicator;
If written, only
a
bit is important (others are ignored) this bit allows
user to control the relay via RS-485 interface
07h
1
08h
1
No
0 ÷ 999999 Peak (drop) value (no decimal point)
10h
Yes
0 ÷ 11
“FrEq”
parameter
in
“inPUt”
menu (input filter):
0
- 10Hz;
1
- 15Hz;
2
- 20Hz;
3
- 30Hz;
4
- 40Hz;
5
- 50Hz;
6
- 100Hz;
7
- 300Hz;
8
- 1kHz;
9
- 3kHz;
10
- 10kHz;
11
- 50kHz
11h
Yes
0 ÷ 19999
“PULSEn”
parameter
in
“inPUt”
menu. Value 0 is interpreted as 1
12h
Yes
0 ÷ 5
“PrEc”
parameter
in
“inPUt”
menu
0
- “ 0”;
1
- “ 0.0”;
2
- “ 0.00”;
3
- “0.000”;
4
- “0.0000”;
5
- “0.00000”;
13h
Yes
0 ÷ 2
“unit”
parameter
in
“inPUt”
menu
0
-rev./sec.;
1
- rev./min;
2
- rev./hour.;
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