©
CIAS Elettronica S.r.l.
Ed. 2.4
3.4 RS-485 Serial Line
3.4.1 RS-485 / 232 Serial Line Interface
Both the receiver and the transmitter of the PYTHAGORAS barrier are provided with a standard
RS485 serial interface. The communication parameters are as follows:
Mode:
Asynchronous
Half-Duplex
Speed: 9600
b/s
Length: 8bit
Parity:
None
Stop
Bit:
1
3.4.2 RS-485Serial Line Connections
The connection can be "multidrop” type, with many barriers connected in parallel on the same
serial line (Bus configuration). These connections are made by connecting, on terminal block
MS3 of both transmitter and receiver, negative RS485 data (RS-485 - ) to terminal 4 “LO”,
positive RS485 data to terminal 3 “LH”, and the data ground reference conductor to terminal 2
“GND”. To connect a PC to the data line use an RS232 serial interface via an RS 485/232
interface converter, provided with the SW WAVE-TEST software. The power supply for this
converter can be supplied via terminals 1 (+13,8V ) and 2 (GND) on MS4 (Rx) or MS5 (Tx).
Interconnection cable for all RX or TX heads to PC for maintenance using
SW MWA TEST
PIN
Terminal
Block MS3
CONNECTOR
25 pin
(D Type)
on converter
N° N°
Symbol
Function
1 12
+13,8 Power supply (13,8 V ) for 485/232converter
2 9
GND
Data and power ground for 485/232 converter
3 10
LH 485 High data line for RS 485
4 11
LO 485 Low data line for RS 485
3.4.3 Network Configuration and Signal Regeneration
The serial connection between the various heads of the installed barriers must be made using a
screened cable, twisted and with low capacitance
(< 70 pF/m)
e.g. “Belden 9842”. The
network architecture should be of the “BUS” type with a maximum length of 1200m. If it is
necessary to use a star architecture or the maximum length of the cable is greater than 1200m
it will be necessary to use one or more line repeaters (BUS-REP model). IT is then possible to
create different cable configurations:
- full star, - mixed, with bus and star using repeaters/regenerators and multiple BUS-REP
interfaces fig. 11. The total number of devices that can be connected to the line is 32 and for
greater numbers it is necessary to use one or more RS485 line regenerators even if the total
length is less than 1200m. For effective protection against induced interference on the line it is
essential that the screen is connected throughout the length of the cable and that it is connected
to GROUND at only one point, usually at the power supply. When there are many barriers
connected to the line the power for the RS485/RS232 converter must be provided by a local
power supply, located close to the converter and, therefore, the PC.
Installation Manual
Page
42
of
56
PYTHAGORAS
