Black Box LD485A-MP User manual

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© Copyright 1999. Black Box Corporation. All rights reserved.

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AUGUST 1999
ME836A-R3
ME836C-R3
BC00702
FA520A-R2
RS-232 Asynchronous
Multipoint Line Driver
(LD485A-MP)
LD485A-MP
RX TX RTS CD PWR
NORMAL
DLB

3
FCC STATEMENT
FEDERAL COMMUNICATIONS COMMISSION
AND
CANADIAN DEPARTMENT OF COMMUNICATIONS
RADIO FREQUENCY INTERFERENCE STATEMENTS
This equipment generates, uses, and can radiate radio frequency energy
and if not installed and used properly, that is, in strict accordance with the
manufacturer’s instructions, may cause interference to radio
communication. It has been tested and found to comply with the limits for
a Class A computing device in accordance with the specifications in Subpart
J of Part 15 of FCC rules, which are designed to provide reasonable
protection against such interference when the equipment is operated in a
commercial environment. Operation of this equipment in a residential area
is likely to cause interference, in which case the user at his own expense will
be required to take whatever measures may be necessary to correct the
interference.
Changes or modifications not expressly approved by the party responsible
for compliance could void the user’s authority to operate the equipment.
This digital apparatus does not exceed the Class A limits for radio noise emission from
digital apparatus set out in the Radio Interference Regulation of the Canadian
Department of Communications.
Le présent appareil numérique n’émet pas de bruits radioélectriques dépassant les
limites applicables aux appareils numériques de classe A prescrites dans le Règlement
sur le brouillage radioélectrique publié par le ministère des Communications du
Canada.

4
INSTRUCCIONES DE SEGURIDAD
NORMAS OFICIALES MEXICANAS (NOM)
ELECTRICAL SAFETY STATEMENT
INSTRUCCIONES DE SEGURIDAD
1. Todas las instrucciones de seguridad y operación deberán ser leídas
antes de que el aparato eléctrico sea operado.
2. Las instrucciones de seguridad y operación deberán ser guardadas
para referencia futura.
3. Todas las advertencias en el aparato eléctrico y en sus instrucciones de
operación deben ser respetadas.
4. Todas las instrucciones de operación y uso deben ser seguidas.
5. El aparato eléctrico no deberá ser usado cerca del agua—por ejemplo,
cerca de la tina de baño, lavabo, sótano mojado o cerca de una alberca,
etc..
6. El aparato eléctrico debe ser usado únicamente con carritos o
pedestales que sean recomendados por el fabricante.
7. El aparato eléctrico debe ser montado a la pared o al techo sólo como
sea recomendado por el fabricante.
8. Servicio—El usuario no debe intentar dar servicio al equipo eléctrico
más allá a lo descrito en las instrucciones de operación. Todo otro
servicio deberá ser referido a personal de servicio calificado.
9. El aparato eléctrico debe ser situado de tal manera que su posición no
interfiera su uso. La colocación del aparato eléctrico sobre una cama,
sofá, alfombra o superficie similar puede bloquea la ventilación, no se
debe colocar en libreros o gabinetes que impidan el flujo de aire por los
orificios de ventilación.
10. El equipo eléctrico deber ser situado fuera del alcance de fuentes de
calor como radiadores, registros de calor, estufas u otros aparatos
(incluyendo amplificadores) que producen calor .

5
INSTRUCCIONES DE SEGURIDAD
11. El aparato eléctrico deberá ser connectado a una fuente de poder sólo
del tipo descrito en el instructivo de operación, o como se indique en el
aparato.
12. Precaución debe ser tomada de tal manera que la tierra fisica y la
polarización del equipo no sea eliminada.
13. Los cables de la fuente de poder deben ser guiados de tal manera que
no sean pisados ni pellizcados por objetos colocados sobre o contra
ellos, poniendo particular atención a los contactos y receptáculos donde
salen del aparato.
14. El equipo eléctrico debe ser limpiado únicamente de acuerdo a las
recomendaciones del fabricante.
15. En caso de existir, una antena externa deberá ser localizada lejos de las
lineas de energia.
16. El cable de corriente deberá ser desconectado del cuando el equipo no
sea usado por un largo periodo de tiempo.
17. Cuidado debe ser tomado de tal manera que objectos liquidos no sean
derramados sobre la cubierta u orificios de ventilación.
18. Servicio por personal calificado deberá ser provisto cuando:
A: El cable de poder o el contacto ha sido dañado; u
B: Objectos han caído o líquido ha sido derramado dentro del
aparato; o
C: El aparato ha sido expuesto a la lluvia; o
D: El aparato parece no operar normalmente o muestra un cambio en
su desempeño; o
E: El aparato ha sido tirado o su cubierta ha sido dañada.

6
RS-232 ASYNCHRONOUS MULTIPOINT LINE DRIVER (LD485A-MP)
TRADEMARKS
All applied-for and registered trademarks are the property of their
respective owners.

7
RS-232 ASYNCHRONOUS MULTIPOINT LINE DRIVER (LD485A-MP)
CONTENTS
1. Specifications. . . . . . . . . . .............................8
2. Introduction . . . . . . . . . . .............................10
3. Installation . . . . . . . . . ...............................11
3.1 Jumper and Switch Configuration ...................11
3.2 DCE/DTE Configuration...........................17
3.3 Typical Application . ..............................24
Appendix: Pinning ....................................29

8
RS-232 ASYNCHRONOUS MULTIPOINT LINE DRIVER (LD485A-MP)
1. Specifications
Interface —(1) asynchronous RS-232 port (DTE/DCE selectable),
(1) asynchronous RS-584 port
Connectors —(1) DB25S, female RS-232 port, (1) four-wire terminal block
RS-485 port
Pins Supported —RS-232 port: TD, RD, RTS, CTS, CD, DTR, DSR, SG,
and FG, RS-485 port: TXA, TXB, RXA, RXB
Data Rate —0 to 64 Kbps, transparent to data
Indicators —(5) LEDs (TX, RX, RTS, CD, and PWR)
Temperature — Operating : 32 to 122 °F (0 to 50 °C), Storage : -4to158°F
(-20 to 70 °C)
Humidity —0 to 95% relative humidity, non-condensing
Mean Time Between Failures —Approximately 180,000 hours (ground
benign environment)
Operation —Point-to-Point or Multipoint, Half or Full Duplex, Transparent
to data, Selectable RTS to CTS delay, DTE or DCE configurable RS-232
port, Normal or loopback operation
Timeout Delay —1 msec, 100 msec, or 1 sec (for the RS-485 driver enabled
by data feature)
Power —Wall-mount transformer, 115 VAC, 8.5 watts or 230 VAC, 8.5
watts
Size —Standalone unit: 1.8”H x 5.5”W x 8.5”D (4.5 x 13.9 x 21.5 cm),
Rackmount card: 4.7”H x 7.4”L (11.9 x 18.8 cm)
Weight —Standalone unit (unit only): 1 lb. (454 g), Power supply only:
0.5 lb. (227 g)

9
RS-232 ASYNCHRONOUS MULTIPOINT LINE DRIVER (LD485A-MP)
Typical Speed Versus Distance —(4-wire point-to-point 26 AWG twisted
pair)
Speed Distance
1,200 bps 4.0 miles
2,400 bps 3.0 miles
4,800 bps 2.3 miles
9,600 bps 1.7 miles
19,200 bps 1.2 miles
38,400 bps 0.9 miles
64,000 bps 0.75 miles
NOTE
Speed and distances will depend on actual operating conditions.

10
RS-232 ASYNCHRONOUS MULTIPOINT LINE DRIVER (LD485A-MP)
2. Introduction
The LD485A-MP Line Driver is an RS-232 to RS-485 interface converter
that operates in much the same way as a modem. It allows an RS-232
device to transmit data over much longer distances than is normally
possible (up to 4 miles at 1200 bps). The advantage of the LD485A-MP
over other line drivers and modems is that it can also operate in multipoint
applications. Depending on the operating environment, as many as 64
devices can be linked together using twisted-pair cable.
The LD485A-MP can be jumpered for a user-selectable port timeout.
After the last character is sent from one of the ports and a specified period
of time passes (1 msec, 100 msec, or 1 second), the LD485A-MP disables any
transmission from that port. This timeout would be used in a multipoint
application to prevent one port from monopolizing the line. For example,
if one line driver was still enabled and no data was being sent, the other line
drivers would not be able to transmit or receive data until the one driver
was disabled. Thus, the line would be tied up, with no useful data
communication taking place. The port timeout feature keeps the line free
by disabling inactive ports.
Additional features include a manual loopback test to check the system
wiring for both the RS-232 and RS-485 interfaces, and transient protection
on the RS-485 interface to help prevent damage due to voltage transients
on the data line.
Although designed specifically to connect to other LD485A-MP line
drivers, the RS-485 port may be connected to any device with an RS-422 or
RS-485 interface. This would be useful in an industrial application, for
example, where RS-485 and RS-422 devices would be connected to the
same LD485A-MP.
The LD485A-MP is available in standalone and rackmount versions. The
rackmount card (part number ME836C-R3) is designed to be installed in
the multi-function rack (part number RM700).
A cable and adapter are included with each Driver.

11
RS-232 ASYNCHRONOUS MULTIPOINT LINE DRIVER (LD485A-MP)
3. Installation
This section describes the jumper and switch functions for configuring the
LD485A-MP. See Figure 3-1 for the component locations. Section 3.1
gives a description of the jumper and switch settings. For a description of
the DCE setup, see Section 3.2 . For a description of the DTE setup, see
Section 3.3 .
Installation consists of the following steps:
1. Set each of the six jumpers/switches as per your application.
2. Connect the LD485A-MP devices together as shown in Figures 3-4
through 3-7 .
3. Apply power.
3.1 Jumper and Switch Configuration
NOTE
In order to make it easier for you to locate the jumper and switch settings
in Tables 3-1 and 3-2, the following descriptions are preceded by a
number. These numbers are identical to the numbers listed for that
function in Tables 3-1 and 3-2.
1. DTE/DCE Configuration
A DIP shunt is used to select DTE or DCE configuration. For the LD485A-
MP to appear as a DTE device, put the DIP shunt jumper in socket XW1B.
For the LD485A-MP to appear as a DCE device, put the DIP shunt jumper
in socket XW1A/
2. Frame Ground/Signal Ground
Jumper W7 ties signal ground to frame ground. The position is left open at
the factory. If signal ground is to be connected to frame ground, solder a
100-ohm, 1/2-watt resistor in location W7. A wire jumper may also be used.
Take care to ensure that ground circulating currents are limited to
acceptable levels.

12
RS-232 ASYNCHRONOUS MULTIPOINT LINE DRIVER (LD485A-MP)
3. Half/Full Duplex Operation
Jumper W8 selects half-duplex or full-duplex operation. Set W8 to the
HALF position for half-duplex operation. Set W8 to the FULL position for
full-duplex operation.
NOTE
When the jumper W9 is in the ON position and jumper W15 is in the A-B
position, the RS-485 driver is always turned on to enable transmission of
data. Therefore, half-duplex transmission cannot be performed. See #5
for an explanation of the RS-485 driver.

13
RS-232 ASYNCHRONOUS MULTIPOINT LINE DRIVER (LD485A-MP)
Figure 3-1. PCB Layout.
J1
W7
J3
PWR TX CD RTS
TXA
TXB
RXA RXB
TB1
RX
S1 IN = LOOPBACK MODE
OUT = NORMAL MODE
UNTERM TERM
50ms 5ms 0ms
VR1
S2
ON
1msA 100msB
1 sec
C
W9 CTS DELAY
HALF FULL
FULL OR HALF DUPLEXW8
ON
RS-485 DRIVER DISABLED
W17
A-B DTR ENABLES DRIVER B-C RTS ENABLES DRIVER
W18
DCE
XW1A
DTE
XW1B
A B C
A-B 5ms HALF DUPLEX B-C 50ms TURNAROUND DELAY W16
A-B DTR/RTS/CD ENABLED B-C DATA ENABLED
W15
A B C A B C

14
RS-232 ASYNCHRONOUS MULTIPOINT LINE DRIVER (LD485A-MP)
4. CTS Delay
When the transmitter of a device is first turned on, an unstable carrier
signal is transmitted for several milliseconds. If data was sent during this
period, it would be received as distorted information. Setting a CTS delay
on the LD485A-MP allows the communications link to settle down before
data can be sent.
a. LD485A-MP as DCE
When the LD485A-MP is configured as a DCE device (DIP shunt in
position XW1A), jumper W9 controls the amount of delay from the time
RTS (jumper W18 in the B-C position) or DTR (jumper W18 in the A-B
position) is received true until CTS is asserted true. To select a CTS delay
period, set jumper W9 to the 0 msec, 5 msec, or 50 msec position.
Regardless of the delay setting selected, when RTS or DTR goes false, CTS
will immediately go false. If jumper W9 is in the “ON” position, CTS will
always be held true.
b. LD485A-MP as DTE
When the LD485A-MP is configured as a DTE device (DIP shunt in
position SW18), CTS is not supported.
5. RS-485 Driver Enable
The LD485A-MP’s RS-485 driver can be set to be enabled one of three
ways: a. by RS-232 control signals, b. by data, or c. constantly on.
a. Driver Enabled by RS-232 Control Leads
If your equipment raises CD, DTR, or RTS, you can set the RS-485 driver
to be enabled by one of these leads. If your equipment does not have the
capability to raise CD, DTR, or RTS, you will need to set the RS-485 driver
to be enabled by data or constantly enabled.
In order for an RS-232 control lead to enable the RS-485 driver, W15
must be in position A-B and W9 must be set for 0, 5, or 50 ms.
• When the RS-232 port is selected as DTE (DIP shunt in the XW1B
position), the RS-485 driver will be enabled when CD (pin 8 of the RS-
232 connector) goes true.

15
RS-232 ASYNCHRONOUS MULTIPOINT LINE DRIVER (LD485A-MP)
• When the RS-232 port is selected as DCE (DIP shunt in the XW1A
position) and jumper W18 is in the A-B position, DTR enables the RS-
485 driver. When jumper W18 is in the B-C position, RTS enables the
driver.
b. Driver Enabled by Data
The RS-485 driver can also be enabled without requiring an RS-232 control
lead to be asserted. When jumper W15 is placed in the B-C position, the
driver is enabled when data is received on the RS-232 port of the LD485A-
MP. As soon as the first bit of the first character is received at the RS-232
port, the RS-485 driver is enabled and an internal timer is started. Each
time a “one to zero” transition occurs in the data, the timer is reset. When
the timer times out, the RS-485 driver is disabled. Jumper W17 allows this
timeout delay to be set for 1 msec, 100 msec, or 1 second (see #7 below).
c. Driver Constantly Enabled
The RS-485 driver can be constantly enabled by setting jumper W9 to the
ON position.
6. Half-Duplex Turnaround Delay
When operating in half-duplex mode (jumper W8 in the HALF position),
the LD485A-MP adds a small delay each time it stops transmitting data and
prepares to receive data. This delay allows the RS-485 interface and
transmission line time to stabilize, thus reducing the possibility of garbled
data being received at the end of a message.
When jumper W16 is in the A-B position, 5 msec of delay is added. This
amount of delay is sufficient for most applications. If you have a long
transmission line or many LD485A-MP devices connected in a network, you
may need to place W16 in the 50 msec (B-C) position.

16
RS-232 ASYNCHRONOUS MULTIPOINT LINE DRIVER (LD485A-MP)
7. RS-485 Interface Terminated or Unterminated
Some distortion on the twisted-pair line may be caused by impedance
mismatch from the different devices connected to the line. To help
eliminate this type of distortion, the RS-485 interface can be terminated
with a resistor network at the receiver input pins (RXA and RXB) via switch
S2. When S2 is placed in the “TERM” position, the resistor network is
connected across the line. When S2 is placed in the “UNTERM” position,
no connection to the resistor network is made and the line is not
terminated.
a. Point-to-Point
When only two devices are connected to the line in a point-to-point
application, each device should have the termination network connected to
the line. Set switch S2 to the “TERM” position.
b. Multipoint
For multipoint applications, switch S2 should be in the “UNTERM”
position on all the LD485A-MP devices in the network except for the two
units at the extreme opposite locations on the line. The extreme opposite
devices are the two devices that have the greatest cable length between
them, which may not necessarily be the devices that are physically located
the farthest apart. These two units should be set in the “TERM” position
(see Figures 3-4 and 3-5 ). If any of the other LD485A-MPs were
configured as “terminated,” the amount of distortion could increase—
possibly causing errors in the data being transmitted.
6. Normal/Loopback Operation
The Normal/Loopback switch is a two-position pushbutton switch extending
through the front panel. The Normal position permits normal operation of
the LD485A-MP. The loopback position allows data coming into the
LD485A-MP to be sent back out the same port. This is for testing the
connection between the LD485A-MP and the device attached to each port.
a. Normal
When this switch is in the normal mode, data is passed through the
LD485A-MP from the RS-232 port to the RS-485 port and vice versa.

17
RS-232 ASYNCHRONOUS MULTIPOINT LINE DRIVER (LD485A-MP)
b. Loopback
When set to the loopback mode, any data received at the RS-485 port will
be transmitted back out the RS-485 port and any data received at the RS-
232 port will be transmitted back out the RS-232 port.
3.2 DCE/DTE Configuration
This section contains block diagrams ( Figures 3-2 and 3-3 ) and jumper and
switch settings ( Tables 3-1 and 3-2 ) for DCE/DTE operation. For a detailed
description of the jumpers and switches, see Section 3.1 .
W17
W16
W9
RS-485
DRIVER
DATA RECEIVED
ENABLES RS-485
DRIVER CIRCUIT
CBA
ENABLE
TX
W15
TXA
TXB
RS-485
RECEIVER
RXA
RXB
HALF DUPLEX
TURNAROUND
DELAY CIRCUIT
CARRIER
DETECT
CIRCUIT
RS-232
DRIVER
ENABLE
W8
FULL HALF
CD
CD
RD
RTS
RX
RTS
C
B
A
TD RS-232
RECEIVER
50 msec
ON
5 msec
0msec
CTS
DTR
DSR ON
W18
Figure 3-2. Simplified Functional Block Diagram (DCE
Operation).

18
RS-232 ASYNCHRONOUS MULTIPOINT LINE DRIVER (LD485A-MP)
Table 3-1. DCE Jumper Settings.
NOTE
In order to make it easier for you to locate the jumper and switch settings
in Section 3.1, the following descriptions are preceded by a number.
These numbers are identical to the numbers listed for that function in
Section 3.1.
Function Jumper Requirements
1. Configure RS-232 port XW1 in A position
as DCE
2. Signal ground connected
to frame ground
• Connected (soldered in place) W7 is IN (100-ohm, 1/2 watt resistor)
• Not connected W7 is OUT
3. Half or full duplex operation.
• Full duplex W8 in FULL position
• Half duplex W8 in HALF position
4. CTS delay
• Yes W9 in 0 ms position
W9 in 5 ms position
W9 in 50 ms position
• No W9 in ON position
(no delay, CTS always true)

19
RS-232 ASYNCHRONOUS MULTIPOINT LINE DRIVER (LD485A-MP)
Table 3-1. DCE Jumper Settings (continued).
Function Jumper Requirements
5. Enable RS-485 driver
a. RS-485 driver enabled
by RS-232 control leads
• by DTR W9 in 0 ms position
W9 in 5 ms position
W9 in 50 ms position
W15 in A-B position
W18 in A-B position
• by RTS W9 in 0 ms position
W9 in 5 ms position
W9 in 50 ms position
W15 in A-B position
W18 in B-C position
b. RS-485 driver enabled W15 in B-C position
by data
• Disable timeout delay 1 msec—W17 in A position
100 msec—W17 in B position
1 sec—W17 in C position
c. RS-485 driver constantly W9 in ON position
enabled
6. Half duplex turnaround
delay
• 5 msec turnaround delay W8 in HALF position
W16 in A-B position
• 50 msec turnaround delay W8 in HALF position
W16 in B-C position

20
RS-232 ASYNCHRONOUS MULTIPOINT LINE DRIVER (LD485A-MP)
Table 3-1. DCE Jumper Settings (continued).
Function Jumper Requirements
7. RS-485 interface terminated
or unterminated
• Terminated S2 in TERM position
• Unterminated S2 in UNTERM position
8. Normal or loopback
operation
• Normal mode S1 in NORMAL position
• Loopback mode S1 in LOOPBACK position