Black Box LD485A-HS User manual

CUSTOMER
SUPPORT
INFORMATION
Order toll-free in the U.S. 24 hours, 7 A.M. Monday to midnight Friday: 877-877-BBOX
FREE technical support, 24 hours a day, 7 days a week: Call 724-746-5500 or fax [phone]
Mail order: Black Box Corporation, 1000 Park Drive, Lawrence, PA 15055-1018
Web site: www.blackbox.com • E-mail: [email protected]
SEPTEMBER 1999
ME837A-R2 ME837AE
ME837C-R2 ME838A-R2
ME838AE ME838C-R2
BC00702 FA520A-R2
LD485A-HS
LD485A-HS Card
LD485A-HS Opto-Isolated
LD485A-HS Isolated Card
LD485A-HS OPTO-ISOLATED
TX RX CD RTS PWR
NORMAL
DLB
RX TX RTS CD
DCE
DTE
LD485A-HS
TX RX CD RTS PWR
NORMAL
DLB
RX TX RTS CD
DCE
DTE

FCC AND IC STATEMENTS
FEDERAL COMMUNICATIONS COMMISSION
AND
INDUSTRY CANADA
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 Industry Canada.
Le présent appareil numérique n’émet pas de bruits radioélectriques dépassant les limites
applicables aux appareils numériques de la classe A prescrites dans le Règlement sur le
brouillage radioélectrique publié par Industrie Canada.

LD485A-HS and LD485A-HS Opto-Isolated
Contents
Chapter Page
1. Specifications...................................................................................................1
2. Introduction ....................................................................................................3
3. Installation.......................................................................................................4
3.1 Jumper and Switch Configuration.........................................................4
3.1.1 DTE/DCE Configuration..........................................................4
3.1.2 Frame Ground/Signal Ground ................................................4
3.1.3 Half/Full-Duplex Operation.....................................................5
3.1.4 CTS Delay...................................................................................7
3.1.5 RS-485 Driver Enable.................................................................7
3.1.6 Half-Duplex Turnaround Delay ...............................................8
3.1.7 RS-485 Interface Terminated or Unterminated ......................8
3.1.8 Normal/Loopback Operation ..................................................9
3.1.9 RS-485 Interface Line Biased (Fail-Safe)..................................9
3.2 DCE Configuration/DTE Configuration............................................10
3.3 Typical Applications .............................................................................18
Appendix A: Pinning ........................................................................................25

1
CHAPTER 1: Specifications
Optical Isolation: ME838A-R2, ME838AE, ME838C-R2 only
Interface — (1) asynchronous RS-232 port (DTE/DCE selectable);
(1) asynchronous RS-485 port with improved surge protection and
switch-selectable line termination or line bias
Connectors — (1) DB25, female—RS-232 port;
(1) four-wire terminal block (TB1)—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 115 Kbps, transparent to data
Indicators — (5) LEDs: TX, RX, RTS, CD, and PWR
Temperature
Operating — 32 to 122° F (0 to 50° C)
Storage — -4 to 158° F (-20 to 70° C)
Humidity — 0 to 95% relative humidity, noncondensing
MTBF — Approximately 180,000 hours (ground benign environment)
Power — PS154 (for use with ME837A-R2, ME838A-R2): Input—120V, 60 Hz,
20W; Output—AC 17VCT, 0.7A; PS154E (for use with ME837AE, ME838AE):
Input—230V, 50 Hz, 20W; Output—AC 17VCT, 750 mA
Size — Standalone Unit: 1.8"H x 5.5"W x 8.5"D (4.6 x 14 x 21.6 cm)
Rackmount Card: 7.4"L x 4.7"W (18.8 x 11.9 cm); 0.6 inches thick (1.6 cm)
Weight — Standalone Unit: 1 lb. (0.5 kg);
Power supply only: PS154—0.4 lb. (0.2 kg), PS154E—1.1 lb. (0.5 kg)
1. Specifications

2
LD485A-HS and LD485A-HS Opto-Isolated
Operation — Point to Point or Multipoint
Half or Full Duplex
Transparent to data
Selectable RTS-to-CTS delay with option to
inhibit CTS if CD is present (DCE)
DTE or DCE configurable RS-232 port
Normal or loopback operation
Timeout Delay — 0.15, 0.7, 2, 7, or 70 msec (for the RS-485 driver enabled by
data feature)
Typical Speed Versus Distance — (4-wire point-to-point 26-AWG twisted pair)
SPEED DISTANCE
1200 bps 4 miles (6.4 km)
2400 bps 3 miles (4.8 km)
4800 bps 2.3 miles (3.7 km)
9600 bps 1.7 miles (2.7 km)
19,200 bps 1.2 miles (1.9 km)
38,400 bps 0.9 mile (1.4 km)
64,000 bps 0.75 mile (1.2 km)
115 Kbps 0.4 mile (0.6 km)
NOTE: Speed and distances will depend on
actual operating conditions.

3
CHAPTER 2: Introduction
The LD485A-HS is an RS-232-to-RS-485 interface converter that operates in
the same manner as a modem. It allows an RS-232 device to transmit data over
much longer distances than is normally possible (up to 4 miles—6.4 km—at
1200 bps). The advantage of the LD485A-HS 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 opto-isolating models (ME838A-R2, ME838AE, ME838C-R2) protect one
segment of your extended network from problems that arise on the other.
Inside the RS-232↔485/422 Opto-Isolator/Converter, optical isolation
circuitry converts electrical signals to light and back again, to keep signal
noise and ground loops from crossing between segments of your RS-485
installation. That means the electrical noise from your factory floor won’t
affect your office communications, and the difference in ground potential
between buildings won’t damage your sensitive equipment.
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-HS line drivers,
the RS-485 port may be connected to any device with an RS-422 or RS-485
interface. For example, this would be useful in an industrial application where
RS-485 and RS-422 devices would be connected to the same LD485A-HS.
The LD485A-HS is available in standalone and rackmount versions. The
rackmount cards (part numbers ME837C-R2 and ME838C-R2) are designed
to be installed in the multi-function rack (part number RM005).
A 6-ft. DB25 male/DB25 female extension cable and a serial AT adapter
(DB9 female/DB25 male) are included with the ME837A-R2, ME837C-R2,
ME838A-R2, and ME838C-R2.
2. Introduction

4
LD485A-HS and LD485A-HS Opto-Isolated
This section describes the jumper and switch functions for configuring the
LD485A-HS. See Figure 1 (page 6) for the component locations.
To install your LD485A-HS:
1. Set each of the ten jumpers/switches for your application.
2. Connect the LD485A-HS devices together as shown in Figures 5
through 8 (pages 19–22).
3. Apply power. (PS154 or PS154E, depending on which LD485A-HS you
have. See Chapter 1 for more information.)
3.1 Jumper and Switch Configuration
NOTE
As you read this section, refer to Tables 1 and 2. Table 1 (page 11) lists
DCE jumper settings, and Table 2 (page 16) lists DTE jumper settings.
3.1.1 DTE/DCE C ONFIGURATION
A DIP shunt is used to select DTE or DCE configuration. For the
LD485A-HS to appear as a DTE device, put the DIP shunt jumper in socket
XW1B. For the LD485A-HS to appear as a DCE device, put the DIP shunt
jumper in socket XW1A.
3. Installation

5
CHAPTER 3: Installation
3.1.2 F RAME G ROUND /S IGNAL G ROUND
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.
Care must be taken to ensure that ground circulating currents are limited
to acceptable levels.
3.1.3 H ALF /F ULL -D UPLEX O PERATION
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
Section 3.1.5 for an explanation of the RS-485 driver.

6
LD485A-HS and LD485A-HS Opto-Isolated
Figure 1. Layout of the Printed Circuit Board.
K K
K K K
DS5 RX
DS2
CD/RTS
DS1
RTS/CD
DSR4
TX
DS3
PWR
DELAY
D - 5ms E - 35ms
S1
W17
W17 DRIVER ENABLE HOLD A - 70ms B - 7ms C - 2ms D - 0.7ms
E - 0.15ms
BC
A
W19
BC
A
W15 A-B = RTS/CD ENABLED B-C = DATA ENABLED
W9 30 mesc
10 mesc
0 mesc
ON
A-B RTS/CTS B-C RTS/CTS/CD
W5A
B C
W15
W8
ABC
ABCDE A
BCDE
AW16
W8 A-B = 2 WIRE B-C = 4 WIRE W16 TURNAROUND
A = 0ms B = 0.1ms C = 1ms
R49/W7
1 2 3 4
P2
O N O N
BIASTERM
XW1A DCE
TB1
XW1B DTE
W18
ABC
J1
TATBRARB

7
CHAPTER 3: Installation
3.1.4 CTS D ELAY
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-HS allows the communications link to settle down before data can be
sent.
LD485A-HS as DCE
When the LD485A-HS is configured as a DCE device (DIP shunt in position
XW1A), jumper W9 controls the amount of delay from the time RTS (jumper
W5 in the A-B position) is received true until CTS is asserted true. If W5 is in
the B-C position, CTS will be inhibited if an RS-485 carrier is present when
RTS is raised. To select a CTS delay period, set jumper W9 to the 0-, 10-, or
30-msec position. Regardless of the delay setting selected, when RTS goes
false, CTS will immediately go false. If jumper W9 is in the “ON” position,
CTS will follow RTS.
LD485A-HS as DTE
When the LD485A-HS is configured as a DTE device (DIP shunt in position
XW1B), CTS is not supported.
3.1.5 RS-485 D RIVER E NABLE
The LD485A-HS’s RS-485 driver can be set to be enabled one of three ways: by
RS-232 control signals, by data, or constantly on.
Driver Enabled by RS-232 Control Leads
If your equipment raises CD 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 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, 10, or 30 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.
• When the RS-232 port is selected as DCE (DIP shunt in the XW1A
position), RTS enables the driver.

8
LD485A-HS and LD485A-HS Opto-Isolated
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-HS.
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. The time begins its
“time out” on a low (0) to high (1) transition of data. When the timer times
out, the RS-485 driver is disabled. Jumper W17 allows this timeout delay to be
set for 0.15, 0.7, 2, 7, or 70 msec.
NOTE
There is a limitation to using this “DATA ENABLES DRIVER” feature. At
data rates above 64 Kbps, the first character in the data stream will be
garbled by the LD485A-HS. If higher data rates are required, transmit a
<break> if possible, or a <nul> character before each message. This will
enable the RS-485 driver, activate the timer, and allow the message to be
transmitted without errors. The receiving device will need to ignore the
first character received.
Driver Constantly Enabled (4 Wire Only)
The RS-485 driver can be constantly enabled by setting jumper W9 to the
ON position.
3.1.6 H ALF -D UPLEX T URNAROUND D ELAY
When operating in half-duplex mode (jumper W8 in the HALF position),
the LD485A-HS 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.
The turnaround delays are 0 (W16 in position A), 0.1 msec (W16 in position
B), 1 msec (W16 in position C), 5 msec (W16 in position D), and 35 msec
(W16 in position E).
3.1.7 RS-485 I NTERFACE T ERMINATED OR U NTERMINATED
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

9
CHAPTER 3: Installation
resistor network is made and the line is not terminated.
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.
Multipoint
For multipoint applications, switch S2 should be in the “UNTERM” position
on all the LD485A-HS 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 5 and 6). If any of
the other LD485A-HSs were configured as “terminated,” the amount of
distortion could increase—possibly causing errors in the data being
transmitted.
3.1.8 N
ORMAL /L OOPBACK O PERATION
The Normal/Loopback switch (S1) is a two-position pushbutton switch
extending through the front panel. The Normal position permits normal
operation of the LD485A-HS. The Loopback position allows data coming into
the LD485A-HS to be sent back out the same port. This is for testing the
connection between the LD485A-HS and the device attached to each port.
Normal
When this switch is in the normal mode, data is passed through the
LD485A-HS from the RS-232 port to the RS-485 port and vice versa.
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.
3.1.9 RS-485 I NTERFACE L INE B IASED (F AIL -S AFE )
If S3 is in the Off position, there is no line bias. If S3 is in the On position,
there is line bias.

10
LD485A-HS and LD485A-HS Opto-Isolated
3.2 DCE/DTE Configuration
This section contains block diagrams (Figures 2 and 4) and jumper and
switch settings (Tables 1 and 2) for DCE/DTE operation. For a detailed
description of the jumpers and switches, see Section 3.1.
Figure 2. Simplified Functional Block Diagram (DCE Operation).
RS-232
RECEIVER
TD TXA
TXB
RS-485
DRIVER
TX
ENABLE
RS-232
DRIVER
ENABLE
RS-485
RECEIVER
RD
CD
DSR ON
RX
RTS
DATA RECEIVED
ENABLES RS-485
DRIVER CIRCUIT
HALF-DUPLEX
TURNAROUND
DELAY CIRCUIT
CARRIER
DETECT
CIRCUIT
CD
CTS
RXB
RXA
W17 W15
W8
W16
W9
W5
HALFFULL
BCA
A
B
C
ON
30 msec
10 msec
0 msec
RTS
Opto-Isolated barrier
in ME838 models

11
CHAPTER 3: Installation
Table 1. DCE Jumper Settings
NOTE
For additional information on the jumper requirements, see Section 3.1.
FUNCTION JUMPER REQUIREMENTS
1. Configure RS-232 port as DCE XW1 in A position
2. Signal ground connected to frame ground
•Connected W7 is IN (solder your own 100-ohm,
1/2-watt resistor in place)
•Not connected W7 is OUT
3. Half- or full-duplex operation
•Full duplex W8 in FULL position (4 wire, A-B)
•Half duplex W8 in HALF position (2 wire, B-C)
4. CTS delay
•Yes W9 in 0-ms position
W9 in 10-ms position
W9 in 30-ms position
•No W9 in ON position
(no delay, CTS follows RTS)

12
LD485A-HS and LD485A-HS Opto-Isolated
Table 1. DCE Jumper Settings (continued)
FUNCTION JUMPER REQUIREMENTS
5. Enable RS-485 driver
a. RS-485 driver enabled by RS-232
control leads
•by RTS W15 in A-B position and
W9 in 0-ms position
W9 in 10-ms position
W9 in 30-ms position
b. RS-485 driver enabled by data W15 in B-C position and
•Disable timeout delay W17 msec
A70
B7
C2
D 0.7
E 0.15
c. RS-485 driver constantly enabled W9 in ON position
6. Half-duplex turnaround delay W8 in HALF position and
•0-msec turnaround delay W16 in position A
•0.1-msec turnaround delay W16 in position B
•1-msec turnaround delay W16 in position C
•5-msec turnaround delay W16 in position D
•35-msec turnaround delay W16 in position E

13
CHAPTER 3: Installation
Table 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
9. RS-485 Interface Line Biased (Fail- S3 Off No line bias
Safe), Receive S3 On Line biased
NOTE: If line bias is on, the
RS-485 CD will ALWAYS be on.

14
LD485A-HS and LD485A-HS Opto-Isolated
Figure 3. Line Bias. S2 shows the line termination when
“Term” is selected. S3 shows line bias when “Bias” is selected.
Rx
S3 S2
+5V
S3
-
+
Tx

15
CHAPTER 3: Installation
Figure 4. Simplified Functional Block Diagram (DTE Operation).
NOTE
The delay settings for W9 apply only to the CTS output of the LD485A-
HS. Since CTS is not used when the LD485A-HS is configured as a DTE
device, placing jumper W9 in either the 0-, 10-, or 30-msec position will
allow the CD input to enable the RS-485 driver. When jumper W9 is in the
ON position, the CD input has no affect on the RS-485 driver.
RS-232
RECEIVER
RD TXA
TXB
RS-485
DRIVER
TX
DTR ON
DATA RECEIVED
ENABLES RS-485
DRIVER CIRCUIT
HALF-DUPLEX
TURNAROUND
DELAY CIRCUIT
CD
W17
W15
W16
W9
A
B
ON
30 msec
10 msec
0 msec
CD
CTS
DSR NOT USED
NOT USED
RX
RS-232
DRIVER
ENABLE
RS-485
RECEIVER
TD
RTS
RTS CARRIER
DETECT
CIRCUIT
RXB
RXA
W8
HALF FULL
C
Opto-Isolated barrier
in ME838 models

16
LD485A-HS and LD485A-HS Opto-Isolated
Table 2. DTE Jumper Settings
NOTE
For additional information on the jumper requirements, see Section 3.1.
FUNCTION JUMPER REQUIREMENTS
1. Configure RS-232 port as DTE XW1 in B position
2. Signal ground connected to
frame ground
•Connected W7 is IN (100-ohm, 1/2-watt
resistor soldered in place)
•Not connected W7 is OUT
3. Half- or full-duplex operation
•Full duplex W8 in FULL position (4 wire, A-B)
•Half-duplex W8 in HALF position (2 wire, B-C)
4. CTS delay CTS not supported
5. Enable RS-485 driver
a. RS-485 driver enabled by W15 in A-B position and
RS-232 lead CD W9 in 0-ms position
W9 in 10-ms position
W9 in 30-ms position

17
CHAPTER 3: Installation
Table 2. DTE Jumper Settings (continued)
FUNCTION JUMPER REQUIREMENTS
b. RS-485 driver enabled by data W15 in B-C position and
•Disable timeout delay W17 msec
A70
B7
C2
D 0.7
E 0.15
c. RS-485 driver constantly enabled W9 in ON position
6. Half-duplex turnaround delay W8 in HALF position and
•0-msec turnaround delay W16 in position A
•0.1-msec turnaround delay W16 in position B
•1-msec turnaround delay W16 in position C
•5-msec turnaround delay W16 in position D
•35-msec turnaround delay W16 in position E
7. RS-485 interface terminated
or unterminated
•Terminated S2 in TERM position
•Unterminated S2 in UNTERM position
8. Normal or loopback operation
a. Normal mode S1 in Normal position
b. Loopback mode S2 in Loopback position