1
RCS770
USB / RS-485 / RS-232 converter
User Manual
23.5.2006
V1.0
INTRODUCTION
RCS770 is a general-purpose serial converter equipped with a USB port, RS-232 port and two RS-485 ports.
Conversion can be done in all directions. Alternatively, this converter can act as a RS-485 repeater allowing
more RS-485 devices to be used, since one bus can normally hold 32 devices. The two RS-485 ports can be
configured to act as a single full-duplex RS-422 port or a four-wire RS-485 port.
USB, RS-232 and RS-485 sections are galvanically isolated from each other, which will eliminate ground
loops and give more tolerance against disturbances and overvoltages. However, the two RS-485 buses are
not isolated from each other.
If RCS770 is connected to a computer via USB, it creates a virtual serial port that can be used just like an
ordinary port. Every converter has an individual serial number, and the converter will retain the same COM
port number even if plugged into a different USB port on the same computer. This increases reliability.
RCS770 is able to pass various serial protocols, including Nokeval SCL, Modbus ASCII, Modbus RTU, and
HART. The RS-485 direction is changed automatically, no handshake lines are required.
RS-485 bus is attached via screw terminals, avoiding the need to make solder joints on field.
SPECIFICATIONS
USB port
Version: USB 1.1 or 2.0
Interface chip: FTDI FT232R
Power consumption: < 200 mA
Connector: USB-B (A-B cable included)
RS-485 ports
Baud rates 300…230400 bit/s, except
as a repeater 1200…
115200.
Data bits 5…8
Parity All supported
Stop bits 1, 1.5 or 2 on USB, 1 on
RS-232
Bus length 1000 m max
Devices on bus max 32 standard devices or
128 1/4 load devices
Load 1/4 load (128 devices of
this kind can exist on the
same bus)
Transmitter enable Automatic
RS-232 port
Connector: D9 male (DTE) (null modem
cable for PC included)
Baud rates: 1200, 2400, 4800, 9600,
19200, 38400, 57600,
115200
Handshake lines: Not controllable, linked
internally
External power supply
Note: external power supply is not necessary when
the USB is used.
Voltage: 8…28 VDC
Current: <200 mA
General
Dimensions: 70x85x60 mm + connectors
Oper. temperature: -30...60 °C
Galvanic isolation: Yes, 2kV AC/DC
EMC
EMC immunity EN 61326
EMC emissions EN 61326 class B
2
CONVERSION MODE
The conversion mode and other settings are done with jumpers. To access them, the enclosure has to be
opened. Insert a small flat blade screwdriver between the lid and the bottom part of the enclosure left or right
side and pull the lid off.
The converter is factory pre-set as a USB–485 converter, all baud rates allowed. RS-485 buses are
terminated and have fail-safes on.
Every conversion mode has a page of its own. After these, there are some pages about installing the USB
drivers and other additional information.
Connectors
Conn Purpose
J3 RS-485 bus 2, or RS-422 bus Tx
J4 RS-485 bus 1, or RS-422 bus Rx
J8 An external power supply can be connected here,
see page 10
J7 An external power supply can be connected here
J6 RS-232 port
J2 USB port
Indicators
LED Purpose
D1 This converter is powered up. USB drivers are
working.
D2 This converter is receiving data from PC via USB
D3 This converter is sending data to PC via USB
Jumpers
Jumper Purpose
J1 RS-485 bus 2 termination and fail-safe
J5 RS-485 bus 1 termination and fail-safe
J14 Connects the power supply of the bus devices and this converter together, see page 10.
J11
Baud rate and bit format selection. Not used when USB is used.
J13 Programming connector for the microcontroller. The middle pins must be jumped.
J10 and J12 Conversion mode. Modes are explained on the following pages.
J9 Closed when 485–485 repeater, open otherwise.
3
4 3 2 1 4 3 2 1 3 2 1
J7
J6
J2
J3 J4 J8
J1
J5
J10
J12
J13
J11
J9
J14
D1
D2 D3
1200 2400 4800 9600 19200 38400 57600 115200 8N1, 7E1, 7O1, 7N2 8E1, 8O1, 8N2, 9N1
USB – RS-485
Jumpers
• To set in USB – RS-485 mode, set J10 and J12 according to the picture.
• J1 and J5 define the 485 bus termination, see page 12.
• J14 controls the power supply options, see page 10.
• J11 and J9 are not used.
Connections
• USB is connected to a computer. See page 11 on drivers.
• RS-485 buses J3 are J4 equal. Any or both of them may be used. See page 12.
• No external power supply is required, but J8 can be used to power up the RS-485 devices connected in
connectors J3 and J4. The power supply is routed from J8 to J3 terminal 1 and J4 terminal 1.
4
Power
supply
(optional)
4 3 2 1 4 3 2 1 3 2 1
J7
J6
J2
J3 J4 J8
J1
J5
J10
J12
J13
J11
J9
J14
D1
D2 D3
USB
RS-485
device
C
D1D0
+ C +
USB – RS-422
Jumpers
• Set J10 and J12 according to the picture.
• J1 and J5 define the 485 bus termination, see page 12.
• J14 controls the power supply options, see page 10.
• J11 and J9 are not used.
Connections
• USB is connected to a computer. See page 11 on drivers.
• J3 and J4 are the RS-422 bus. This device transmits at J3 and receives at J4.
• No external power supply is required.
5
Power
supply
(optional)
4 3 2 1 4 3 2 1 3 2 1
J7
J6
J2
J3 J4 J8
J1
J5
J10
J12
J13
J11
J9
J14
D1
D2 D3
USB
RS-422
device
C
T1T0
+ C +
R1R0
Rx-
Rx+
Tx-
Tx+
Common
Power
USB – RS-232
Jumpers
• The USB–232 mode is selected with jumpers J9, J10, and J12 according to the picture.
• J1, J5, J11, and J14 have no effect.
Connections
• USB is connected to a computer. See page 11 on drivers.
• How to use the RS-232 bus, see page 15.
• No external power supply is needed.
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4 3 2 1 4 3 2 1 3 2 1
J7
J2
J3 J4 J8
J1
J5
J10
J12
J13
J11
J9
J14
D1
D2 D3
USB
J6
RS-232
RS-232 – RS-485
Jumpers
• To select 232–485 mode, set jumpers J9, J10, and J12 according to the picture.
• J1 and J5 select the 485 bus terminations, see page 12.
• J14 controls the power supply flow onto the bus, see page 10.
• J11 is used to control the baud rate and bit format:
Connections
• RS-485 buses J3 and J4 are equal. Any or both of them may be used. See page 12.
• RS-232 bus is explained on page 15.
• This converter must be powered externally on J7 or J8, see page 10.
7
4 3 2 1 4 3 2 1 3 2 1
J6
J2
J3 J4 J8
J1
J5
J10
J12
J13
J11
J9
J14
D1
D2 D3
RS-485
device
CD1D0 +
RS-232
Mascot
J7
+-
1200 2400 4800 9600 19200 38400 57600 115200 8N1, 7E1, 7O1, 7N2 8E1, 8O1, 8N2, 9N1
RS-232 – RS-422
Jumpers
• 232–422 mode is selected with jumpers J9, J10, and
J12 according to the picture.
• J1 and J5 define 422 bus termination, see page 14.
• J14 controls power supply options, see page 10.
• J11 selects the baud rate and bit format, see picture
below.
Connectors
• J3 is RS-422 Tx and J4 is Rx. See page 14.
• RS-232 is explained on page 15.
• An external power supply must be connected in J7 or
J8, see page 10.
8
4 3 2 1 4 3 2 1 3 2 1
J6
J2
J3 J4 J8
J1
J5
J10
J12
J13
J11
J9
J14
D1
D2 D3
RS-232
+-
RS-422
device
C
T1T0+R1R0
Rx-
Rx+
Tx-
Tx+
Common
Power
Mascot
J7
1200 2400 4800 9600 19200 38400 57600 115200 8N1, 7E1, 7O1, 7N2 8E1, 8O1, 8N2, 9N1
RS-485 REPEATER
Jumpers
• 485 repeater mode is selected with jumpers J9, J10, and J12 according to the picture.
• J1 and J5 define the 485 bus termination, see page 12.
• J14 controls the power supply options, see page 10.
• J11 selects the baud rate and bit format:
Connectors
• J3 and J4 are the RS-485 buses. Data on either bus is repeated onto the other.
• This converter must be powered up from an external supply brought to connector J7 or J8. See page 10.
9
4 3 2 1 4 3 2 1 3 2 1
J6
J2
J3 J4 J8
J1
J5
J10
J12
J13
J11
J9
J14
D1
D2 D3
RS-485
device
C
D1D0
+
J7
RS-485
device
C
D1D0
+
Mascot
9V
1200 2400 4800 9600 19200 38400 57600 115200 8N1, 7E1, 7O1, 7N2 8E1, 8O1, 8N2, 9N1
SUPPLY VOLTAGE
Supply voltage for RCS770
If USB is used, RCS770 does not need other power supply for itself. If USB is not used, an external power
supply is needed.
The external supply is connected to connector J7 or J8. If you use J8, read the section ”Jumper J14” below.
J7 is a 1.3 mm DC jack and it accepts voltage between 8 and 28 VDC. If 230 VAC socket is available,
Nokeval recommends Mascot 8311-9V-3635 AC/DC adaptor, available separately.
Supply voltage for the bus devices
It is sometimes convenient to build the RS-485 bus with a four wire cable consisting of common, power
supply, and two data lines. This is why RCS770 has four terminals on each bus connector: one of the
terminals is reserved for supply voltage. RCS770 does not generate this supply voltage and it must be
brought to connector J8 or J7. If you use J7, read the section ”Jumper J14” below.
RCS770 itself does not care which way the bus devices are powered. This power supply routing is provided
only to make the cabling easier.
The voltage can be anything as long as it does not exceed 30 VDC because there is a 33 V varistor
protecting from voltage surges.
Jumper J14
If jumper J14 is open, J7 is used to provide the supply voltage for RCS770 itself and J8 is used to provide the
supply voltage for the RS-485 bus devices.
If jumper J14 is closed, these two circuits are interconnected. You can bring the external power supply at
either J7 or J8 and in both cases the same power supply will be used for both RCS770 and the bus devices.
10
3 24 3
Supply
24V
3 241 2 11
+-
USB
Mascot
RS-232
485 circuits
232 circuits
J14
J3 J4 J8
J7
Separate supply for
RCS770 and bus
devices
Common supply
J14
Isolation
USB
Installing the drivers
There are two ways to install the USB drivers.
Found New Hardware wizard
If you just plug in the device, the Found New Hardware
wizard will be triggered.
The drivers can be obtained from:
• Nokeval Software CD or
• Windows Update (XP only)
• Downloaded from the USB chip manufacturer http://www.ftdichip.com/, VCP drivers for FT232R.
The wizard is launched twice: the first drivers are the USB drivers, and the second driver creates a virtual
serial port in Windows.
Pre-installing the driver
Another way to install the drivers is to run a setup file in the Nokeval Software CD before plugging in the
device. The device can then be plugged in and all is done.
When the drivers are successfully installed, the power indicator on RCS770 should light up.
Virtual serial port
The USB driver creates a virtual COM port in the next unused port number. To find out which port we got, go
to the Device Manager (Control Panel, System, Hardware, Device Manager). In the device tree, expand
branch Ports, and you should see e.g. USB Serial Port (COM3).
If you double click the port, you can change its properties. The most useful thing is the ability to change the
port number (Port Settings, Advanced).
USB hubs
If RCS770 is connected to a USB hub, the hub should have a power supply of its own as always if any of the
devices draw more than 100 mA current.
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RS-485 BUSES
The RS-485 bus has two data lines delivering the data. The polarity of the voltage between the lines defines
whether a bit indicating 'zero' or 'one' is being transferred. Several devices can be attached to the bus. Only
one of them can transmit at a time, while the others listen. Thus the communication is half-duplex.
Connections
RCS770 has four terminals for each RS-485 bus: D1, D0, Common, and +. The first three of these form the
RS-485 bus and the fourth, optional line allows easy power supply wiring for the bus devices.
D1, D0, and Common are wired one-to-one to the other devices on the bus. D1 and D0 are the data lines.
Common is needed to remove potential differences between the devices, and it may serve as the negative
power supply wire too.
Some older devices do not have a Common terminal available. In that case, connect the lines D1 and D0
only. If RCS770 is not wanted to terminate, set the jumpers J1 and J5 to ”2-wire” position instead of ”Not
term”.
The two buses (J3 and J4) are equal. The data coming from USB or RS-232 is transmitted on both of the
buses, and data coming from either of the buses is delivered to USB or RS-232.
There has been quite rich use of names for the data lines. Even EIA/TIA recommended ”A” and ”B” have
been used with two meanings. Nokeval has decided to use the names defined by Modbus standard, D1 and
D0. The table below lists
common names for the
lines:
D1 D0
+ -
B A
A B
Cable
The D1 and D0 should be of a twisted pair, minimum diameter 0.5 mm (24 AWG). In a noisy environment a
shielded cable should be used, the shield grounded at one end only.
A daisy-chain wiring topology is recommended. If braches or stubs are made, they should be only a couple of
meters long.
Terminating and fail-safes
If the bus is longer than some dozens of meters or if high baud rates are used, the bus must be terminated in
order to avoid reflecting the signal from the bus ends. The reflections will cause bit errors.
Fail-safe resistors are needed to ensure the correct state on the bus when nobody is transmitting. They
create va voltage of at least 0.2 V between lines D1 and D0. Each bus should have only one device failsafing.
The termination and fail-safes of RCS770 are
controlled with jumpers J1 (for bus at J3) and
J5 (for bus at J4). Factory setting is both failsafes and termination on.
The termination provided by RCS770 is of AC type: the terminating resistor (110 ohms) has a capacitor in
series (1 nF). The fail-safes are 500 ohms from D1 line to +5V and 500 ohms from D0 line to ground.
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Not te r m Ter m inated Ter m + FS 2-w ir e
RCS770
3 2 1
J3 J4
J1
J5
RS-485
device
RS-485 bus
RS-485
device
CD1D0CD1D0
4 3 2 1 4 3 2 1
RS-485 bus
Direction control
USB
When a computer sends data via USB, the RS-485 transmitters are enabled automatically. When the last bit
has been transmitted, the transmitters are immediately disabled in order to be able to receive data from the
RS-485 bus.
RS-232
When some data is sent to RCS770 via RS-232, RCS770 buffers it one byte duration. After that, it activates
the RS-485 transmitters, waits another 1/2 bytes and then starts transmitting the data on the bus. When the
last bit has been transmitted, the RS-485 transmitter is disabled to allow receiving data.
Because the direction is controlled automatically, the RS-232 handshake lines are not used.
RS-485 repeater
RCS770 listens to both buses. When data is received from either bus, the transmitter of the other bus is
enabled and the data is repeated there 1.5 bytes delayed. When there is no incoming data for 1/2 bytes, the
transmitter is disabled and both buses are listened to again.
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RS-422 BUS
RS-422 bus consists of two separate wire pairs, one for each direction. This allows full duplex
communications.
Connections
The wire pair carrying data from RCS770 to the
other device is connected in connector J3, and
the other pair is connected in connector J4. In
addition, a Common or potential equalisation
wire should be connected from connector J4
terminal 2 to the other device.
There are various names for the RS-422 lines,
but the table below lists some:
Terminal J3.3 J3.4 J4.3 J4.4
Modbus TXD1 TXD0 RXD1 RXD0
Old Tx+ Tx- Rx+ Rx-
Cable
The cable should consist of twisted pairs so that
TXD1 and TXD0 form one pair and RXD1 and
RXD0 another. The minimum recommended diameter for the cable is 0.5 mm (24 AWG). In a noisy
environment a shielded cable should be used, the shield grounded at one end only.
Terminating and fail-safes
In RS-422 bus, both wire pairs have always one transmitter enabled. There is no benefit in terminating or failsafing the transmitting end of the wire pair. So it is recommended to enable the termination and fail-safes of
the receiving end only: in RCS770, jumpers J1 should be set ”Not term” and J5 ”Term + FS”.
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Not te r m Term inate d Ter m + FS
3 2 1
RS-422 device
D1D0
4 3 2 1
Power supply
+-3 2 14
RCS770
J3 Tx J4 Rx J8
CD1D0 +
Rx Tx
RS-232 PORT
Pins
The RS-232 port of RCS770 is of ”DTE” or ”data terminal equipment” type, similar to the port on PC's. So
RS-232 devices can be connected to RCS770 with similar cable that would be used between the device and
a PC.
If RCS770 is connected to a PC using an RS-232 bus, a cross-connected (also called as ”null-modem”)
cable must be used. It is enough to connect pins 2-3, 3-2, and 5-5.
Pin Name Purpose Direction
1 DCD Carrier detected In
2 RxD Data receive In
3 TxD Data transmit Out
4 DTR RCS770 is ready Out
5 Gnd Ground
6 DSR Other device is ready In
7 RTS RCS770 requests to send Out
8 CTS Other device allows to send In
9 RI Telephone ringing In
Handshake lines
RCS770 is intended to be primarily a USB-RS-485 or RS-232-RS-485 converter, not USB-RS-232, although
possible. Consequently the RS-232 handshake lines are not controllable, but they are interconnected as
follows:
DTR is connected to DCD and DSR. RTS is connected to CTS.
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1 2 3 4 5
6 7 8 9
TROUBLESHOOTING
The indicator lights are useful in troubleshooting. Unfortunately the Tx and Rx indicators work only when USB
is used.
Step 1: Drivers and supply voltage
Is indicator D1 lit?
• Yes: go to step 2.
• No and USB is used: reinstall the drivers.
• No and USB is not used: check that there is an external power supply connected in J7 or J8. If the power
supply is connected in J8, make sure that jumper J14 is closed.
Step 2: Transmission
Start the application on PC. Examine, if the Tx indicator is blinking. If not, the application is using a wrong
COM port probably. This test is not applicable if USB is not used.
Step 3: Reception
If Tx is blinking but Rx is not, your RS-485 device is not responding. Check that it is powered up, the
connections are correct, and the baud rate and serial address are correct.
Step 4: Bus voltage RS-485
Use a multimeter to measure the voltage between data lines D1 and D0. It should be 0.2 to 5.0 volts, D1
being the positive. If the voltage is 0, the bus is short-circuited or there are no fail-safes.
Measure the voltage at each bus device and pay attention that the polarity is correct (D1 positive).
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Yrittajakatu 12
FIN-37100 Nokia
Finland
Tel +358 3 3424800
Fax +358 3 3422066
www.nokeval.com
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