The converter takes its low power supply from the RS232 PC output port and does not need extern power. A low power sensor can also be powered (few mA) from the PC through the RS485 connector via pin 4 and/or 9.
An extra cable can be plugged between the PC and the converter if needed. The cable female/male must be an 1 to 1 type and must have all connections wired to insure suply to the converter.
If only the RX, TX and GND lines are used on the RS232 side,
6 to 32Vdc
can be supplied on the RS485 side on pen 4 and/or 9 to feed to the
converter.
RS232 female connector:
1
DCT
Data Carrier Detect
2
RX
Receive Data
3
TX
Transmit Data
4
DTR
Data Terminal Ready
5
GND
Ground
6
DSR
Data Set Ready
7
RTS
Request To Send
8
CTS
Clear To Send
9
RI
Ring indicator (Not Connected)
RS485 male connector:
1
nc
Not Connected
2
A
RS485 line A, internally connected to pin 8
3
B
RS485 line B, internally connected to pin 7
4
V+
Output or input supply or not used, internally connected to pin 9.
5
0V
Ground through 100 Ohm resistor
6
nc
Not Connected
7
B
RS485 line B, internally connected to pin 3
8
A
RS485 line A, internally connected to pin 2
9
V+
Output or input supply or not used, internally connected to pin 4.
There is no termination resistor (120R) installed. Line A and
B are
internally connected to respectivelly GND and +5V, both through an 1K
resistor.
This can be suppressed by opening the enclosure and removing jumper RA
and RB.
Application examples:
One RS485 sensor or new RS485 hardware design can be
connected to
one of the PC RS232 com port.
Start a communication terminal or your own written software
application,
select then the correct baud rate (matching the RS485 one), the right
communication
port, hardware handshake (data transport control) if the converted
needs
to be powered via the PC or no handshake if the power is externally
applied
(via pin 4 and/or 9 (both are internally connected)). No special
sofware
protocol needs to be implemented on the RS485 side with one device.
Just
as simple as the usal RS232 protocol.
More than one PC can be connected to the same RS485 device. They each
need a converter on their RS232 comport to be able to communicate with
the RS485 device, in turns.
Be aware that strange enough, C or VB software applications do not drive the RS232 control lines right the same way on different Window platform 95/98/ME/XP. So if the converter power needs to come from the PC, one has to do some checking on this. Especially RTS, CTS and DTR.
Multiple RS485 connections on one PC.
First same as above, connect all lines A and all lines B together.
With short connections and upto 32 RS485 devices it should not give any
trouble even with no termination resistor. This time a kind of protocol
needs to be implemented to be able to address specifically one of the
RS485
devices.
Two or more PC's connected together over a long distance.
This funny application does for sure not arise the quality of a good
network, but is a simple way to connect PC's together over several
hundreds
of meters in the half duplex mode. Just plug a converter to each PC and
connect the two lines A and B and for a long distance the two GND
together.
The last are for free if you take care of shipping !