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15.3 RS-485 serial interface
15.3.1 Hardware
The data line connecting the measurement and
control devices by means of the RS-485 interface
must be carried out in bus topology (not star
topology).
Use two-core cable with a cross section of at least
0.5 mm
2
.
The maximum length of the lines is 1,000 m.
Connecting the interface
•
Connector pin assignment (9-pole sub-D-
connector)
– pin 1: shielding (necessary for line lengths >
100 m. Only to be connected at one side)
– pin 3: data +.
– pin 8: data -.
The bus function of the device must be adjusted by
jumpers (in the plug).
•
If the device is used as MASTER (device
number 32), carry out the following adjustment:
– jumper 4-7
•
If the device is used as SLAVE (device
number 1-31), carry out the following adjustment:
– no jumpers
•
If the device is used as last SLAVE (device
number 1-31), carry out the following adjustment:
– jumper 4-7
Data transfer format
– 9,600 baud
– 1 start bit
– 1 stop bit
– 8 data bits
– no parity
Software
Data transmission consists of several parts:
– the function request
– the information
– the end of the data transmission.
The data transmission starts with calling the
demanded device. The devices connected to the bus
are identified by the device number which must be
selected at the single devices.
The function request for starting a transmission is
"line feed" (LF). Then the corresponding device
number is transmitted. After that, "carriage return"
(CR) is transmitted, which always indicates the end
of a function request or data transmission.
The called device answers with the device code (see
device codes). The device code contains the type of
the device and the operating status.
If the operation mode is "automatic" and no alarm
indication is present, a Conex DIS-2Q controller
answers with code "54". If an indication is present,
the code "5C" is transmitted. Now you can read the
reason of the alarm from the corresponding list,
which can be called up with "$". Set the
corresponding bit to acknowledge the alarm.
Transmit the corresponding function number to call
the demanded function. Now the device transmits
the contents of this function as a two-digit or four-
digit binary number and again completes the
transmission with "CR". Now you can change the
settings of this function. An example of this dialog is
given below.
Operations set of the transmission
If you change a value via the interface, the
corresponding numbers are transmitted as four-digit
binary numbers without decimal point.
Character Hexadecimal Function
LF
0A H
Line feed, the
demanded device is
selected
CR
0D H
Input is finished
$
24 H
Function selection, see
functions list
C
43 H
The selected function
is changed
H
41 H
The function selected
before is called again
Decimal
Hexadecimal
ASCII character
0
30 H
0
1
31 H
1
2
32 H
2
3
33 H
3
4
34 H
4
5
35 H
5
6
36 H
6
7
37 H
7
8
38 H
8
9
39 H
9
10
3A H
:
11
3B H
;
12
3C H
<
13
3D H
=
14
3E H
>
15
3F H
?
