Amplicon 485HF9 User manual

Model 485HF9
Page 1
MODEL 485HF9
PLUG-IN
SIGNAL
LEVEL
ADAPTOR
9 PIN RS-232
TO RS-422/485
This Instruction Manual is supplied with the Model 485HF9 Adaptor to provide the user with sufficient information to
utilise the purchased product in a proper and efficient manner. The information contained has been reviewed and is
believed to be accurate and reliable, however Amplicon Liveline Limited accepts no responsibility for any problems
caused by errors or omissions. Specifications and instructions are subject to change without notice.
Model 485HF9 Instruction Manual Part Nº 859 864 34 Issue A4
© Amplicon Liveline Limited
Prepared by D. Field
Approved for issue by A.S. Gorbold, Operations Director

Model 485HF9
Page 2
DECLARATION OF CONFORMITY
AMPLICON LIVELINE LIMITED
CENTENARY INDUSTRIAL ESTATE
HOLLINGDEAN ROAD
BRIGHTON BN2 4AW UK
We de
clare that the product(s) described in this Instruction Manual are
manufactured by Amplicon Liveline Limited and perform in conformity
with the following standards or standardisation documents:
Electro Magnetic Compatibility (EMC):
EMC Directive 89/336/EEC
LVD Directive 73/23/EEC
CE Directive 93/68/EEC
Jim Hicks, I. Eng, MIEIE
Managing Director
Amplicon Liveline Limited

Model 485HF9
Page 3
PARA SUBJECT PAGE
1 INTRODUCTION 4
1.1 General Description 4
1.2 Technical Features 4
1.3 What the Package Contains 5
1.4 The Amplicon Warranty Covering the Model 485HF9 Adaptor 5
1.5 Contacting Amplicon Liveline Ltd for Support or Service 6
1.5.1 Technical Support 6
1.5.2 Repairs 6
2 INSTALLATION INSTRUCTIONS 7
2.1 Requirements of Host Equipment 7
2.2 Connections to Model 485HF9 Adaptor 7
2.2.1 RS-232 Connections on 9 way D Connector 7
2.2.2 RS-422/485 Connections on 8 way Pluggable Terminal Strip 8
2.3 Configuration of Model 485HF9 Adaptor Options 8
2.4 Power Requirements 10
2.4.1 Connecting the Amplicon Mains Adaptor 11
2.5 Full Duplex / Half Duplex Operation 11
2.5.1 Selection of Full / Half Duplex 12
2.5.2 Selection of Transmit Enable Control Signal 12
2.5.3 Selection of Local Echo On/Off in Half Duplex Operation 13
2.6 Transmission Line Termination 13
2.6.1 Network Biasing Resistors 14
2.7 Software Installation 15
2.8 Installation Testing 15
3 APPLICATION INFORMATION 16
3.1 Applicable Standards 16
3.2 RS-232 Application Notes 16
3.2.1 Electrical Levels 17
3.2.2 9/25 Way Adaptors 17
3.3 RS-422 / 485 Application Notes 17
3.3.1 RS-422 / 485 Parameters 18
3.3.2 Cabling of RS-422 / 485 Bus 18
3.3.3 Multi-drop Applications 19
3.3.4 Bus Termination 20
4 TESTING AND TROUBLESHOOTING 21
4.1 Basic Testing and Fault Isolation 21
4.1.1 Testing with the Application Software 21
4.1.2 Loop-back Testing Using a Simple BASIC Program 21
5 TECHNICAL INFORMATION 23
5.1 Technical Specification 23
5.1.1 Electrical Specification 23
5.1.2 Physical/Environmental Specification 23
5.2 Optional Accessories 24
5.2.1 U.K. Mains Adaptor Power Supply 24
5.2.2 Universal Mains Adaptor Power Supply 24
FIG Nº TITLE PAGE
2.1 RS-232 Connections 7
2.2 RS-422/485 Connections 8
2.3 Configuration Options 9
2.4 Power Supply Connections for Single 485HF9 Adaptor 10
2.5 Power Connections for Multiple Model 485 Adaptors 11
2.6 Connections for Full and Half Duplex Operations 12
2.7 External Transmitter Enable Connections 13
2.8 Network Biasing Resistors 14
3.1 DTE Adaptor - 9 Way to 25 Way 17
3.2 RS-232/422/485 Parameters 18
3.3 RS-422 Connected in Broadcast Mode 19
3.4 RS-485 Connected in Multi-drop, Half Duplex Mode 20
4.1 Terminal Links for Loop-back Test 21
A.1 Model 485HF9 Circuit Schematic 24
MODEL 485HF9 MANUAL CONTENTS

Model 485HF9
Page 4
1. INTRODUCTION
1.1 General Description
The Model 485HF9 Adaptor is a compact, plug-in unit providing bi-directional conversion of
serial data communications signals between the following standards:-
The Model 485HF9 Adaptor is equipped with a 9 way, female D type connector. Many RS-232
devices are similarly equipped, and when properly configured and powered, the adaptor can be
plugged into the appropriate port to convert the transmit and receive signals to RS-422/485
levels. RS-232 hardware handshaking lines are looped back, and the RS-232 Request To Send
(RTS) control line can be used for RS-485 transmission turnaround if required. The unit is
supplied for the RS-232 host device configured as Data Terminal Equipment (DTE).
The data conversion process changes only electrical levels, and the pin-out configuration is in
accordance with the appropriate standards. The adaptor itself is not considered as DTE or
DCE, and where these terms are used, they apply to the RS-232 equipment to which the Model
485HF9 Adaptor is connected.
RS-485 multi-drop operation allows up to 32 devices to be connected in a simple network on a
single serial bus. The transmitter has a tri-state output and may be disabled to allow reception
over the same wire pair. The high impedance state (transmitter disabled) is commanded from
an external control signal or from the host computer RTS line.
DC power for the Model 485HF9 Adaptor must be applied from an external source. The DC
power lines plus the RS-422/485 data and control signals are connected through a pluggable 8
way screw terminal assembly at the free end of the Adaptor.
EMC Considerations
In order to maintain compliance with the EMC directive, 89/336/EEC, it is mandatory that the
final system integrator uses good quality screened cables for external connections. It is up to
the final system integrator to ensure that compliance with the Directive is maintained. Amplicon
Liveline offers a series of good quality screened cables for this purpose. Please contact our
sales staff.
1.2 Technical Features
•RS-422 or RS-485 compatible
•Multi-drop capability
•Plugs directly into standard 9 pin male connector
•Configured for operation with DTE host
•Single power supply connection. Polarity protected
•Remote connections via pluggable terminal strip
•Compact and versatile
RS-232 RS-422
OR
RS-232 RS-485

Model 485HF9
Page 5
1.3 What the Package Contains
1. The Model 485HF9 Adaptor board with 8 way free socket and the plastic case
disassembled. The plastic case should not be snapped together until any necessary
configuration changes have been made.
The complete 485HF9 Adaptor is supplied under Amplicon order code 909 458 03
Some of the components on the board are susceptible to electrostatic discharge, and
proper handling precautions should be observed. As a minimum, an earthed wrist strap
must be worn when handling the 485HF9 Adaptor outside its protective bag.
Full static handling procedures are defined in British Standards Publication
BSEN100015/BSEN100015-1:1992
When removed from the bag, inspect the board for any obvious signs of damage and
notify Amplicon if such damage is apparent. Do not apply power to a damaged board and
do not plug it into the host computer. Keep the protective bag for possible future use in
transporting the module.
2. This 485HF9 Instruction / Reference manual. Amplicon part number 859 864 34
Any additional accessories (mating gender changers, power supply etc.) may be packed
separately.
1.4 The Amplicon Warranty Covering the Model 485HF9 Adaptor
This product is covered by the warranty as detailed in the Terms and Conditions stated in the
current domestic or international Amplicon Liveline catalogue.
Changes made in accordance with the guidelines given in this manual will not void this
warranty unless any damage is a direct consequence of mishandling.
DO NOT MAKE ANY MODIFICATIONS TO A PRODUCT THAT IS ON EVALUATION.
! CAUTION

Model 485HF9
Page 6
1.5 Contacting Amplicon Liveline Limited for Support or Service
The Model 485HF9 Adaptor is designed and manufactured by Amplicon Liveline Ltd.
Maintenance is available throughout the supported life of the product.
1.5.1 Technical Support
Should the Model 485HF9 Adaptor appear defective, please check the information in this
manual to ensure that the product is being correctly applied.
If an application problem persists, please request Technical Support on one of the following
numbers:
Telephone: UK 0906 293 0293
Fax: UK 01273 570 215
Internet [e-mail]
www.amplicon.co.uk
1.5.2 Repairs
If the Model 485HF9 Adaptor requires repair then please return the goods enclosing a repair
order detailing the nature of the fault. If the product is still under warranty, which is for a period
of 12 months from the date of shipment, there will be no repair charge unless the fault has
been caused by misuse.
For traceability when processing returned goods, a Returned Materials Authorisation (RMA)
procedure is in operation. Before returning the goods, please request an individual RMA
number by contacting Amplicon Customer Services by telephone or fax on the above numbers.
Give the reason for the return and, if the goods are still under warranty, the original invoice
number and date. Repair turnaround time is normally five working days but the Service
Engineers will always try to co-operate if there is a particular problem of time pressure.
Please mark the RMA number on the outside of the packaging to ensure that the package is
accepted by the Goods Inwards Department.
Address repairs to: Customer Services Department
AMPLICON LIVELINE LIMITED
Centenary Industrial Estate
Brighton, East Sussex
BN2 4AW
England
Calls cost 25p per min from a BT landline. Calls from other services may vary

Model 485HF9
Page 7
2. INSTALLATION INSTRUCTIONS
2.1 Requirements of Host Equipment
The Model 485HF9 Adaptor can be plugged into any device with an RS-232 port terminating in
a 9 way D type male connector (DB-9). If the host device is equipped with a 9 way connector, it
is normally male, and the 485HF9 Adaptor can be directly plugged into this port and held in
position by its jack screws.
In addition to the 9 pin standard, many RS-232 interface connectors comply with the DB-25
standard and two types of 485 Adaptor are available from Amplicon Liveline Ltd to mate with
male or female versions of the DB-25 connector. In addition, DIN, mini-DIN and other types of
connector are sometimes used for RS-232 ports. If the pin connections of the host device
interface are known, then enough information is given in this manual to make up a suitable
adaptor connection cable.
2.2 Connections to Model 485HF9 Adaptor
Connections are made to the Model 485HF9 Adaptor at each end. The RS-232 connections are
automatically made when the Adaptor is plugged into the port, and the RS-422/485 data,
control and power connections must be made through a pluggable 8 way screw terminal
connector assembly at the free end.
2.2.1 RS-232 Connections on 9 way D Connector
The connections conform to the RS-232 adopted 9 way pin-out standard, and are shown in
figure 2.1 below. The diagram shows the connector as viewed from the face of the socket
mounted on the Model 485HF9 Adaptor.
FIGURE 2.1 RS-232 CONNECTIONS
1
6
2
7
3
8
4
9
5
Data Set Ready (DSR)
Request To Send (RTS)
Clear To Send (CTS)
Ring Indicator (RI)
Data Carrier Detect (DCD)
Receive Data (RxD)
Transmit Data (TxD)
Signal Ground (SG)
Data Terminal Ready (DTR)
RS-232 connections on 9 way socket

Model 485HF9
Page 8
2.2.2 RS-422/485 Connections on 8 way Pluggable Terminal Strip
The DC power input, RS-485 transmission turnaround external control signal and RS-422/485
data signal connections are made via an eight way screw terminal connector. The supplied
connector can be unplugged from the Adaptor for ease of making the cables without removing
the Adaptor from the port.
The connections are compatible with other 485 Adaptors in the Amplicon range, and are shown
in figure 2.2 below. The diagram shows the connector as viewed from the top face of the Model
485HF9 Adaptor. The abbreviated function names are printed on the PCB extension below the
fixed part of the connector.
FIGURE 2.2 RS-422/485 CONNECTIONS
2.3 Configuration of Model 485HF9 Adaptor Options
Configuration of the options is undertaken by cutting or bridging solder pad links on the reverse
(non-component) side of the Model 485HF9 Adaptor printed circuit board. The Adaptor as
supplied is configured to suit the majority of applications requiring full duplex operation or half
duplex with echo.
For convenience, the plastic case is supplied in two parts and should only be clipped together
when any configuration changes have been made. Operational tests can be performed before
the case is fitted.
The configuration options listed below are available, and the appropriate connection bridges
are shown in figure 2.3.
J1 Transmit Enable - RTS or External. (Factory configuration is 'External TXEN’)
J2 Receiver termination in or out. (Factory setting is 'IN')
J3 Receive echo on or off. (Factory setting is echo on)
The configuration options are described in more detail in the following paragraphs. For many
applications, no changes need be made, but if re-configuration is required, locate the pad group
1 EN /Transmit Enable
2 GND Ground
3 TX - B Transmit Data
4 TX - A /Transmit Data
5 RX - A’ /Receive Data
6 RX - B’ Receive Data
7 GND Power Ground
8 VDC +5.0 to +13 VDC I/P
RS-422/485 power, data and control connections

Model 485HF9
Page 9
from figure 2.3 which illustrates the non-component side of the printed circuit board. When an
existing link is not needed, cut the copper tie with a craft knife or remove any solder bridge with
a desoldering tool, and make solder links as indicated for the required configuration. The pads
are placed close enough that a solder bridge can be easily made without using wire. Before
applying power to the Adaptor, inspect the changes carefully to ensure that the solder has
properly wetted the pads and that no other bridges have been made.
FIGURE 2.3 CONFIGURATION OPTIONS
EN
J2
GND
J3
J1
GND
VDC
B
A
A’
B’
Transmit Enable
External TXEN
Transmit Enable
RTS
Receive Echo
ON
Receive Echo
OFF
UNLINKED
COPPER
PAD PAIR
PADS WITH
SEVERED
LINK
PADS WITH
SOLDER
BRIDGE
KEY
PADS WITH
SEVERABLE
LINK
RX Line Terminator
IN
RX Line Terminator
OUT
J2
J1J3

Model 485HF9
Page 10
2.4 Power Requirements
The Model 485HF9 Adaptor must be powered from an external power supply providing a
positive output of between +5.0 VDC and +13.0 VDC. This auxiliary power supply unit should
be capable of sourcing at least 100 mA for each 485 Adaptor that it supplies. Within this
constraint, as many 485 Adaptors as are required can be fed from a single supply. The
Amplicon Mains adaptor meets this requirement and the U.K. version is available under order
code 919 135 69. See paragraph 2.4.1 for information on connecting this mains adaptor to the
Model 485HF9 terminals.
The 485HF9 Adaptor is fitted with an eight way pluggable terminal strip at its free end, and the
power supply should be connected to terminals 7 and 8. Terminal 7 is Ground or negative,
terminal 8 is the positive supply. OBSERVE POLARITY when powering the adaptor. If the
polarity is incorrect, the 485HF9 Adaptor will not operate, but is protected against damage. A
wiring diagram for applying power to a single 485HF9 Adaptor is shown in figure 2.4 and the
connections to multiple, parallel powered 485HF9 Adaptors are shown in figure 2.5.
FIGURE 2.4 POWER SUPPLY CONNECTIONS FOR SINGLE MODEL 485HF9 ADAPTOR
When multiple 485 Adaptors are fed from a single supply as in figure 2.5, the grounds of all the
devices on the RS-422/485 bus will be connected together through the common negative
supply line and the internal ground connections of the Adaptors.
POWER SUPPLY
5.0 to 13.0 VDC
–
+
Model
485HF9
Adaptor
EN
1
GND 2
TX 3
TX
4
RX
5
RX 6
GND 7
VDC
8

Model 485HF9
Page 11
FIGURE 2.5 POWER CONNECTIONS FOR MULTIPLE MODEL 485 ADAPTORS
2.4.1 Connecting the Amplicon Mains Adaptor
The optional mains adaptor plugs directly into a 3 pin, 13 A mains socket (U.K. version), or
must be fitted with a suitable plug (International version). The mains supply voltage must be
230 VAC ±10%, 50 Hz. The DC output is by a two wire cable approximately 2 m in length. This
cable is terminated in a moulded connector which must be cut off and discarded. The two wires
can then be parted and stripped back about 6 mm. The black wire is negative and goes to
terminal 7 (GND) of the 485HF9 Adaptor, and the black wire with a white stripe is positive and
goes to terminal 8 (VDC). Section 5.3 gives the Amplicon order codes for the above adaptors.
2.5 Full Duplex / Half Duplex Operation
The Model 485HF9 Adaptor can be used in either full duplex (simultaneous transmission and
reception over two independent wire pairs) or half duplex (sequential transmission or reception
over a single wire pair).
In full duplex operation, a separate transmitter and receiver circuit is employed, and in this
mode the transmitter can be left in its enabled state at all times. In half duplex operation, the
transmitter must be disabled by switching to its high impedance state to allow reception of data
over the same serial lines.
The Model 485HF9 Adaptor is provided with all the data input/output terminals required for full
duplex operation. If half duplex working is required, then the following external and
internal configuration changes must be considered. Also check that the termination
resistor, paragraph 3.3.4, is correctly set for the system in use.
POWER SUPPLY
5.0 to 13.0 VDC
–
+
Model
485HF9
Adaptor
Ground line (–) is connected
internally to RS-232 Ground
Model
485HF9
Adaptor
EN
1
GND 2
TX 3
TX
4
RX
5
RX 6
GND 7
VDC
8
EN
1
GND 2
TX 3
TX
4
RX
5
RX 6
GND 7
VDC
8

Model 485HF9
Page 12
2.5.1 Selection of Full/Half Duplex
In the full duplex position, the serial RS-422/485 signals are transmitted on the wire pair Tx and
/Tx and the incoming signals are received on Rx and /Rx. In half duplex operation, the data
signals are both transmitted and received on the two pairs externally wired in parallel.
FIGURE 2.6 CONNECTIONS FOR FULL AND HALF DUPLEX OPERATION
2.5.2 Selection of Transmit Enable Control Signal
In half duplex operation over a single circuit or a multi-drop arrangement, the transmitter must
be enabled when the device is ready to transmit, and disabled (tri-state) when the device is
ready to receive. Two methods are provided for enabling the transmitter, and the desired
method is selected by the link on J1. (See figure 2.3).
1. External
TXEN
. With the External
TXEN
option selected on J1, the transmit enable is
under the control of a TTL level or RS-232 level signal applied to terminal 1 (/EN) of the
connector strip. This control signal is active low, and is internally pulled down when no
signal is applied. In full duplex or transmit only operation, this control line can be left
open-circuit, when the transmitter will be continuously enabled.
In externally controlled half duplex operation, or any other situation where the transmitter
requires external control, the signal applied to terminal 1 for enabling or disabling the
transmitter must not exceed the following levels:-
ENABLE TRANSMITTER '0' (Active Low) -30 V to +0.8 V ) Input
) Resistance
DISABLE TRANSMITTER 1' +2.4 V to +30 V ) 5 kΩtypical.
Figure 2.7 shows how the external control connection is made.
Model
485HF9
Adaptor
Model
485HF9
Adaptor
Tx (B)
Tx (A)
Rx (A’)
Rx (B’)
Tx/Rx (B)
Tx/Rx (A)
Half Duplex Connection
Transmit and Receive over same circuit
Full Duplex Connection
Separate Transmit and Receive
EN
1
GND 2
TX (B) 3
TX
(A) 4
RX
(A’) 5
RX (B’) 6
GND 7
VDC
8
EN
1
GND 2
TX (B) 3
TX
(A) 4
RX
(A’) 5
RX (B’) 6
GND 7
VDC
8

Model 485HF9
Page 13
FIGURE 2.7 EXTERNAL TRANSMITTER ENABLE CONNECTIONS
In external control, the transmitter enable line can be controlled from a programmable bit on
the host computer. If the computer is equipped with a parallel printer port, then D7 of this port
may be used to control the transmitter. Connect a single wire from pin 9 of the Centronics
compatible connector to the /EN terminal of the Model 485HF9 Adaptor. The program must
clear D7 to transmit or set D7 to receive over the RS-485 interface.
2. RTS Transmit Enable. The transmitter can alternatively be enabled under control of
the RTS (Request To Send) line of the RS-232 host DTE device. See J1 in figure 2.3 for the
appropriate patching.
In normal RS-232 DTE operation, RTS is raised to its ON condition when the device is ready to
commence transmission. In some circumstances, the use of RTS provides a simple means of
enabling the transmitter, however, check overall system timing before using this control
method.
Further information on half duplex and multi-drop operation is given in the applications section
of this manual.
2.5.3 Selection of Local Echo On/Off in Half Duplex Operation
The factory default configuration of link J3 causes the transmitted data can be echoed to the
receiver in half duplex operation. If this echo is not required, the copper link must be severed
and the solder bridge made across the other gap (see paragraph 2.3). This change ensures that
the RS-485 receiver is enabled/disabled in opposite phase to the transmitter.
For full duplex operation, the link J3 must be in its default condition for the receiver to be
continuously enabled. Echo back is not appropriate to full duplex operation.
2.6 Transmission Line Termination
In RS-422 or RS-485 applications, the two wire transmission lines must be properly terminated,
and a single resistor across the receiver input pair normally provides adequate termination.
The Model 485HF9 Adaptor is equipped with a terminator resistor for the receiver input pair,
and this resistor is connected into circuit by the J2 link on the printed circuit board. See figure
2.3. Factory setting is with the receiver input terminator in circuit, but it can be removed from
the circuit by cutting the link as described in paragraph 2.3. Removal of the link is required in
some multi-drop applications.
TXEN
‘0’ Level (or open
circuit) to Enable
‘1’ Level to Disable
Model
485HF9
Adaptor
EN
1
GND 2
TX 3
TX
4
RX
5
RX 6
GND 7
VDC
8

Model 485HF9
Page 14
See the applications section of this manual for a discussion of bus termination.
2.6.1 Network Biasing Resistors
In some instances, particularly in RS-485 multi-drop operation, noise may be detected at the
receiver. In the multi-drop configuration, there can be brief periods when no transmitter is
enabled, and the network is therefore allowed to float. The Model 485HF9 Adaptor is protected
against this condition, but other devices on the network may be susceptible to noise and are
liable to float to a potential that is detected as an input. The programmer can sometimes
overcome this situation by ensuring that the communications protocol flushes the input buffer
until the beginning of the message flag is found.
If this problem is encountered and a software solution is not viable, two extra resistors can be
added externally to the 485HF9 transceiver at one end of the bus, so that the network is biased
to about 1 volt when all transmitters are disabled. The arrangement is shown in figure 2.8.
FIGURE 2.8 NETWORK BIASING RESISTORS
Model
485HF9
Adaptor
R2
120 Ω
180 Ω
+6 to +9 V Supply
180 Ω
Other
RS-485
Device
Other
RS-485
Device
Other
RS-485
Device
SCHEMATIC
180
Ω
180
Ω
TX - RX BUS
+6 to +9 V Supply
WIRING
Model
485HF9
Adaptor
EN
1
GND 2
TX 3
TX
4
RX
5
RX 6
GND 7
VDC
8

Model 485HF9
Page 15
2.7 Software Installation
Software is not supplied with the 485HF9 Adaptor, but a choice of suitable software packages is
available from Amplicon Liveline Ltd. to allow easy integration of serial communications into
the user's application.
The 485HF9 Adaptor connected via an existing RS-232 port will operate in conjunction with
many commercially available communications and data acquisition packages that support RS-
232, RS-422 or RS-485 serial operations. The software should be installed according to the
supplier's instructions, and due note should be taken of the required settings for the
communications channels, and the communications circuit configurations set accordingly.
The following software limitations should be remembered when allocating COM channels:-
MS-DOS 3.2 and below provides support for the first two serial ports only, COM1 and COM2.
MS-DOS 3.3 and above supports COM1, COM2, COM3 and COM4.
Other operating systems allow the use of more than two ports. Check the instructions.
Most BASIC language interpreters/compilers only support COM1 and COM2.
Communications support toolkits such as Amplicon 'COMBIOS' and ‘COMBIOS for Windows’
allow add-on serial ports to several different language compilers.
2.8 Installation Testing
Many applications packages include a self test feature, and when the hardware and software
have been satisfactorily installed, any such test should be performed to check correct
operation.
If no self test is available, or a problem occurs, see the later section 4, 'TESTING AND
TROUBLESHOOTING'.

Model 485HF9
Page 16
3. APPLICATION INFORMATION
As previously noted, many applications packages are designed to support data transfer over
the RS-422 or RS-485 standard serial communications ports. When set up as specified, the
interface will be transparent to the user. However, for special applications, particularly when
use of the RS-485 interface is required, the following notes will be helpful.
3.1 Applicable Standards
The prefix 'RS' signifies Recommended Standard, and the three interface types, RS-232, RS-
422 and RS-485, are all well defined in the appropriate standards publications. The functions
and features of the data interfaces presented by the Model 485HF9 Adaptor generally conform
to normal industry practice employing subsets of the full standards.
The RS-232 serial interface standard is now at revision E and its full title is EIA (Electronic
Industries Association) RS-232-, "Interface Between Data Terminal Equipment and Data
Communication Equipment Employing Serial Data Interchange". Similar European standards
CCITT V.24 and V.28 define an interface which is operationally compatible with RS-232.
The RS-232 connection of the Model 485HF9 Adaptor is for equipment configured as DTE
(Data Terminal Equipment), and the Adaptor has a female connector.
The RS-232 standard specifies a 25 pin connector, but the full 25 connector pins are not
required to support the common functions of RS-232 as used by the Model 485 range of
adaptors, and IBM and other manufacturers frequently adopt a 9 way D connector that provides
all the necessary functionality. The Model 485HF9 Adaptor complies with this adopted pinout
convention. Although three versions of the Amplicon 485 Adaptor are available, there may be
occasions where a 9/25 pin conversion cable or adaptor such as the Amplicon PC-AT Serial
Port Adaptor 909 245 77 is useful. Paragraph 3.2.2 gives the connection details for making up
a suitable converter cable.
The RS-422 interface is defined in the EIA standard RS-422-A, "Electrical Characteristics of
Balanced Voltage Digital Interface Circuits".
As stated, this standard defines the electrical characteristics but does not specify a connector
type or pin-out configuration. The Model 485 Adaptor meets the RS-422 standard electrical
specification with communication via an 8 way terminal strip connector wired as shown in the
installation diagrams.
The RS-485 specification is also published as an EIA standard and is closely allied to the RS-
422. The 485 Adaptor meets the requirements for data signals as laid down in the standard.
3.2 RS-232 Application Notes
RS-232 was approved as a standard interface in 1969. Before and since that time, this
interface in its various revisions has been very popular despite its many shortcomings and
usage outside of its intended role. Most small computers now have an RS-232 interface as
standard, or easily added, and many peripherals and instruments also support this serial
interface, but not all in the same way. Hence an RS-232 application needs careful study of the
host equipment manufacturers connections and methods before the Model 485HF9 Adaptor is
installed. However RS-232 lines are quite safe if wrongly connected, so the experimental use
of a break-out box or 'hit and miss' methods of establishing communication can be employed.

Model 485HF9
Page 17
3.2.1 Electrical Levels
When checking out serial communications circuits, it is useful to know what signal levels to
expect. The specified voltage levels of RS-232 data and control signals are summarised in the
following table:-
Interchange Voltage –3 to –15 +3 to +15
Binary State 1 0
Data Signal Marking Spacing
Control Function OFF ON
Signal Ground is at 0 volts, and the region between –3 and +3 volts is the transition region.
The Model 485 Adaptor will normally be used in close proximity to the RS-232 port, but in a
case where it is not close, the following limits apply. The electrical levels at which RS-232
operates limit the maximum data rate to about 20 kilobaud (sometimes used up to 100 kBd)
and the maximum cable length between transmitter and associated receiver to about 15 m (50
ft)
3.2.2 9/25 way Adaptors
The wiring list in figure 3.1 shows the necessary connections to adapt a 9 way RS-232 port to a
25 way RS-232 port, or vice versa. Due note should be taken of the gender of the mating
connector, and a gender change can be incorporated in the adaptor if required.
FIGURE 3.1 DTE ADAPTOR - 9 Way to 25 Way
3.3 RS-422/485 Application Notes
RS-422 and RS-485 have very similar characteristics, with RS-485 being compatible with, and
offering all the advantages of RS-422 plus some additional capability. RS-422 pre-dated RS-
485 as a standard, but RS-485 is now more popular and used in new system design. For the
485 Adaptor, the on board circuitry for the two modes is identical, the application deciding the
mode of interface operation.
8 DCD
3 Rx D
2 Tx D
20 DTR
7 SIG GND
6 DSR
4 RTS
5 CTS
22 RI
DCD 1
Rx D 2
Tx D 3
DTR 4
SIG GND 5
DSR 6
RTS 7
CTS 8
RI 9
25 WAY PIN-OUTS 9 WAY PIN-OUTS

Model 485HF9
Page 18
3.3.1 RS-422/485 Parameters
The following table in figure 3.2 summarises the principal parameters of the RS-422-B and RS-
485 standards, and shows RS-232 for comparison.
EIA STANDARD RS-232 RS-422-B RS-485
Mode of Operation Single ended Differential Differential
Number of Drivers and
Receivers on line
1 Driver
1 Receiver
1 Driver
10 Receivers
32 Drivers
32 Receivers
Max. Cable Length 15 m 1200 m 1200 m
Max. Data Rate 20 kBd 10 MBd 10 MBd
Max. Common Mode N/A +7 V, –7 V +12 V, –7 V
Driver Voltage ±5 V to ±15 V ±2 V min ±1.5 V min
Driver Load 3 kΩto 7 kΩ100 Ωmin 60 Ωmin
Driver Slew rate 30 V/µs N/A N/A
Driver Output
Short Circuit Limit
500 mA to
Vcc or Ground
150 mA to
Ground
150 mA to Gnd
250 mA to Vcc
Driver Output
Resistance
Power On-N/A
Power Off-300 Ω
Power On-N/A
Power Off-60 kΩ
Power On-120 kΩ
Power Off-120 kΩ
Receiver Input Resistance 3 kΩto 7 kΩ4 kΩ12 kΩ
Receiver Sensitivity ±3 V ±200 mV ±200 mV
Receiver Hysteresis 1.15 V 50 mV 50 mV
FIGURE 3.2 STANDARD RS-232/422/485 PARAMETERS
3.3.2 Cabling of RS-422/485 Bus
RS-232 data transmission rates are specified up to 20 kBd but are sometimes as high as 115
kBd. The Model 485HF9 Adaptor can therefore be used up to 115 kBd and the maximum cable
length of 1200 m will apply at all usable data rates.
RS-422/485 employs a differential method of signal transmission, and each bus cable has to be
a wire pair, preferably twisted and screened to keep induced noise to a minimum. The bus
distribution cable is effectively a transmission line, and appropriate techniques should be used
for installation of the cables. In a multi-drop environment, the cable should be 'looped through'
each device, or if a spur is necessary, the spur length should be kept to a minimum.
If screened cable is used, some thought must be given to the connection of the screen. This
screen should not normally be used as a ground return for non-isolated devices and it is safest
to only connect the screen at a single point to the ground of one device.
The voltage between the grounds of the various devices must not cause the common mode
voltage rating of any device on the bus to be exceeded.

Model 485HF9
Page 19
3.3.3 Multi-drop Applications
RS-422 can provide limited multi-drop capability, using two twisted wire pairs in a broadcast
mode. One wire pair connects one transmitter to multiple receivers, but if duplex operation is
required, only one receiving station can answer back. See figure 3.3.
FIGURE 3.3 RS-422 CONNECTED IN BROADCAST MODE
RS-485 allows multiple (up to 32) transmitters and receivers to be connected in half duplex on
a single twisted wire pair for 'party line' type of communications. See figure 3.4. A method must
be used to stop more than one transmitter being on the line at any time, ensuring that all other
transmitters are in a high impedance state, although the circuit design is such that no damage
will be done to the transceivers if several transmitters are turned on together. In a multiple RS-
485 transmitter installation, the application program controls the data communication
turnaround and the selection of the bus 'talker'.
Two common ways of providing program control are the 'Master / Slave' and 'Token Ring'
methods. The 'Master / Slave' method designates one device on the network as Master, and
this device supervises all transmissions by communicating with each of the Slaves in turn and
offering it a transmission slot. In token ring operation, each device knows its ID neighbour and
only talks directly to this next device. Thus communication only occurs between adjacent pairs
of devices and this makes for a flexible network but can be a more difficult method to
implement.
The Model 485 Adaptor provides a method of communication turnaround by enabling the 'ON'
transmitter using an external control signal or RTS from the RS-232 port. Default condition of
the Model 485 Adaptor enables the transmitter, so that for full duplex operation of RS-422/485
no control signal is required.
Model 485
Adaptor
Model 485
Adaptor
120
Ω
Model
485
Adaptor
Model
485
Adaptor
Model
485
Adaptor
120
Ω
=
Twisted
Wire Pair
Data
Transmitter
Master
Answer-back Tx
EN
1
GND 2
TX 3
TX
4
RX
5
RX 6
GND 7
VDC
8
EN
1
GND 2
TX 3
TX
4
RX
5
RX 6
GND 7
VDC
8
EN
1
GND 2
TX 3
TX
4
RX
5
RX 6
GND 7
VDC
8
EN
1
GND 2
TX 3
TX
4
RX
5
RX 6
GND 7
VDC
8

Model 485HF9
Page 20
FIGURE 3.4 RS-485 CONNECTED IN MULTI-DROP, HALF DUPLEX MODE
3.3.4 Bus Termination
For proper operation of the RS-422/485 bus in full or half duplex, multi-drop or point-to-point
communication, it is recommended that termination is applied to the receiver end of the data
lines.
The simplest form of termination is line-to-line with typically a 120 Ωresistor across the
differential input, and this terminator is available on the Model 485HF9 Adaptor board,
selectable by J1.
In a multi-drop system, the terminator resistor is only required at the device receiver located at
the far end of the cable. If this is in half duplex operation, then both ends of the bus cable are
equipped with receivers (transceivers) so termination is necessary at both ends. Although the
485HF9 Adaptor will drive loads as low as 27 Ω, in general, RS-485 transmitter circuits are
specified as being capable of driving a minimum load resistance of 60 Ω, so no more than two
terminator resistors should be connected to any one bus.
Model
485
Adaptor
120
Ω
Model
485
Adaptor
=
Twisted
Wire Pair
Model
485
Adaptor
120
Ω
Model
485
Adaptor
EN
1
GND 2
TX 3
TX
4
RX
5
RX 6
GND 7
VDC
8
EN
1
GND 2
TX 3
TX
4
RX
5
RX 6
GND 7
VDC
8
EN
1
GND 2
TX 3
TX
4
RX
5
RX 6
GND 7
VDC
8
EN
1
GND 2
TX 3
TX
4
RX
5
RX 6
GND 7
VDC
8