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Note: VOLTAGE LEVEL CONVERTER ONLY, INDEPENDENT OF PROTOCOL.
Module Functionality:
The unit is factory configured to interface to a standard IBM PC RS232 9 pin port with a
“straight through” cable. The unit only uses 2 or 3 lines (plus ground) of the RS232
interface. Rx and Tx are always used. It is possible to permanently drive the RS485
transmitter (used in full duplex mode) or to allow a transmitted character to force the
transmitter to be enabled and allow the reversion to a high impedance output after a fixed
period (See RS485 Transmitter Enable). Some RS232 ports require the CTS and/or the
DSR lines to be enabled. The RS232/485 converter provides 2 pull up resistors to 10V to
allow this.
For full duplex operation the transmit line pair is A1/B1 and the receive line is A2/B2.
For half duplex operation the active line pair is A1/B1.
Termination Resistors (supplied already installed)
R18 is the termination resistor for A2/B2 - the receive line pair for full duplex
communication
R19 is the termination resistor for A1/B1 - the transmit line pair for full duplex
communication, and the line pair used for half duplex communication. The units use
SFR16J resistors and are supplied with 120 ohm resistors. If the unit is not at either end
of a line termination then the resistors should be removed.
Ground Reference Resistors (supplied already installed)
In order to allow RS485 communications across multiple units without violating the
common mode voltage restrictions of the RS485 drivers each unit needs to be referred to
the same ground. (Refer to application note RS-485: A Primer.*) The line pair A1/B1
shield S1 is referenced to ground through a 100 ohm MRS25F resistor, R11. R11 is
mounted internally on sockets and may be removed if so desired. The line pair A2/B2
shield S2 is referenced to ground through a 100 ohm MRS25F resistor, R14. R14 is
mounted internally on sockets and may be removed if so desired.
*Available on request by email from [email protected] or visit
www.weidmuller.ca Æ Products Æ Signal Interface Products Æ Application Notes.
Failsafe Resistors (not supplied)
Although the receivers on the RS232/485 Converter are failsafe, additional failsafe
resistors (SFR16J) may be installed on sockets internal to the unit. Line pair A1/B1 has a
pull up resistor R13 and a pull down resistor R12. Line pair A2/B2 has a pull up resistor
R16 and a pull down resistor R15.
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Failsafe Operation and the 991635/991676/991677
When an input on the RS485 line is not connected to a low impedance source (all the
drivers on the line are in high impedance or not connected) the floating signal may induce
a spurious signal on the RS232 side of RS485 receiver which may in turn lead to spurious
interrupts and erroneous messages received by the UART. Failsafe operation in RS485
means that the inputs have resistor biasing to prevent this condition. The devices used on
the above Weidmuller products all include integral biasing resistors of a approximately
100K. Use of a termination resistor may defeat the inherent failsafe biasing. The user has
two options: Remove the termination resistors which may not be required at lower
transmission frequencies and shorter lengths or installation of additional failsafe resistors
in locations internal to the above units.
It is possible to install these failsafe resistors in each module, but the number of modules
on a network will affect the resistor value (since they are all in parallel) and it becomes
tedious to install all the resistors. Since each module has default failsafe affected only by
the termination resistor, if the module with the termination resistor is removed from the
circuit this internal failsafe would come into operation. It is intuitive that the additional
failsafe resistors should be included only in the two units with line termination resistors.
The calculation of the values for the resistors is based on maintaining 200mV across the
line termination resistor. The network consists of a resistor (R13 or R16) to 5V connected
to the “A” input of the RS485 and to one end of the line termination resistor. The other
side of the line termination resistor is connected to the “B” input of the RS485 input and
to a pull-down resistor (R12 or R15) to ground. These resistors are installed internal to
the Weidmuller units and are mounted in resistor sockets. The voltage across a 120ohm
line termination resistor is given by (120 * 5)/(2R+120) where R is the value of the pullup or pull-down resistors, assuming identical values for the pull-up and pull-down
resistors. This must be greater than 200mV
(120*5)/(2R+120) > 0.2
600> 0.4R+24
1440>R
The lower the value of R, the greater the noise immunity, but the higher the current
drawn by the system. The nearest standard value is 1K2. Since there are 2 resistors in
parallel the effective value under normal circumstances is 600 ohms.
The user should install SFR16J 1K2 resistors in locations R12 and R13 for half-duplex
operations and in R12, R13, R15 and R16 for full duplex operations. The user is required
to remove a side plate of the module housing to access these locations.
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Note:
To determine proper jumper settings, user must refer to the pin out for the RS232 cable being used in
conjunction with the pin out of the RS232 device. Once that is done, the relevant settings may be made by
matching the PIN outs or flow of data using Tables 1 & 5.
Jumper Settings & Functions
Jumper
#
J1
Position 1-2
Position 2-3
Removed
Notes
RS-485 transmitter always
ON / Full Duplex
Auto Enable RS-485
transmitter / Half Duplex
See table 2 & 3 for
more info.
Host DTR Enables RS485 transmitter / Half
Duplex
Data out of module
through PIN 2
Host RTS Enables RS-485
transmitter
/ Half Duplex
Data out of module
through PIN 3
RS-485 transmitter
controlled by DTR or
RTS / Half Duplex
RS-485 transmitter auto
enable or Full Duplex
J4
Data In module through
PIN 3
J5
Host DTR controls RS485 transmitter through
module PIN 4
Host DSR Enabled from
module
PIN 6
Host RTS controls RS-485
transmitter through PIN 7
J2
J3
J6
J7
J8
J9
J10
Host CTS Enabled from
module
PIN 8
Echo Disabled (Half
Duplex)
Full Duplex
See table 2 & 3 for
more info.
Not Allowed
See table 5 for more
info
Data In module through
PIN 2
Not Allowed
See table 5 for more
info.
Host DTR controls RS485 transmitter through
PIN 6
Host DSR Enabled from
module PIN 4
Non DTR controlled /
Full Duplex
See table 2 & 3 for
more info.
Host DSR not Enabled
See table 5 for more
info.
Non RTS controlled /
Full Duplex
See table 2 &3 for
more info.
Host CTS not Enabled
See table 5 for more
info.
Echo Enabled (Half
Duplex)
Not Allowed
See table 2 & 4 for
more info.
See table 2 & 4 for
more info.
Host RTS controls RS485 transmitter through
PIN 8
Host CTS Enabled from
module PIN 7
Full Duplex
Half Duplex
PIN X (on DB9 Connector)
Table 1
RS-485 Configurations
Full Duplex
i.e. Transmitter always enabled.
Table 2
Jumper #
Location
J10
J9
J1
J2
J5
J7
1-2
2-3
1-2
Removed
Removed
Removed
+A1
+A1
S1
S1
-B1
-B1
+A2
+A2
S2
S2
-B2
-B2
Fig 1. Data Flow in Full Duplex operation
3
Half Duplex
Jumper
#
RS-485 transmitter
Auto enable
Baud
R20
rate
Value
1200
1.2M
2400
640K
4800
320K
9600
174K
RS-485
RS-485
Transmitter Transmitter
controlled
controlled
by Host’s
by Host’s
DTR
DTR
through
through
WTL Pin 4 WTL Pin 6
RS-485
Transmitter
controlled
by Host’s
RTS
through
WTL Pin 7
RS-485
Transmitter
controlled
by Host’s
RTS
through
WTL Pin 8
Removed
2-3
Removed
1-2
Removed
2-3
Removed
2-3
(default)
J1
J2
J5
J7
19200
80K
115200
40K
2-3
Removed
Removed
Removed
Removed
1-2
1-2
Removed
Removed
1-2
2-3
Removed
Table 3
Jumper
#
J10
J9
Location
2-3
Echo Enable Echo Disable
Removed
1-2
Table 4
+A1
+A1
S1
S1
-B1
-B1
Fig.2 Information Flow for Half Duplex operation
4
RS-232 Configurations
All references are to the DB9 connector on the Weidmuller module.
PIN functions are determined by the flow of data on PINs 2 & 3 on the Weidmuller RS232
module.
Description
From RS-485 to
RS-232
From RS-232 to
RS-485
Control of RS-485
transmitter by Host
GND
Host Control
Information
Flow
Pin #
Pin #
Jumper settings
Jumper settings
J3/1-2
J3/2-3
Data out of
module (Tx)
Data into module
(Rx)
Control Data into
module (DTR)
Control Data out
of module
J4/1-2
1
2
3
3
2
4
6
5
6
5
4
DSR
DSR Not
Enabled
Enabled
DSR Not
Enabled
Enabled
J6/1-2
Control of RS-485
transmitter by Host
Host Control
Control Data into
module (RTS)
Control Data out
of module
J4/2-3
1
DSR
J6
removed
J6/2-3
7
See half duplex RS485 configuration
When Host requires
DSR enabled
(otherwise remove)
J6
removed
See half duplex RS485 configuration
7
CTS Not
Enabled
J8
removed
9
Not Used
8
8
CTS
Enabled
J8/1-2
Comments
CTS
CTS Not
Enabled
J8
removed
Enabled
J8/2-3
9
When Host requires
CTS enabled
(otherwise remove)
Not used
Table 5
Default Settings:
J2 to J8 /1-2
(IBM PC with direct connection cable)
DTR enabled, DSR and CTS enabled with pull up resistor.
J9/2-3
J10/1-2
Full Duplex
Full Duplex
5
6
7
Specifications subject to change without notice. 99990165 01/03 Printed in Canada
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