1.	Introduction..A Word about Shareware

	1.1	What Shareware is
	1.2	Advantages of Registration.
	1.3	Registration of the ModScan Application
	1.4	Licensing Agreement
	1.5	Warranty
	
2.	ModScan System Requirements

	2.1	Operational Overview
	2.2	System/Cabling Requirements

3.	Installation

	3.1	Making Backups
	3.2	Installing ModScan

4.	Basic Operation

	4.1	MODBUS Protocol
	4.2	Polling Operation
	4.3	Display Parameters

5.	Menu Selections

	5.1	Setup
	5.2	Display Options
	5.3	Monitoring Serial Data
	


6.	Technical Support
	
	6.1	Contacting WinTECH



Introduction..A Word about Shareware
 
What is Shareware

Shareware is a distribution method, not a type of software.
Shareware products may be freely distributed among potential
users with each user given an opportunity to fully evaluate
the software over a specified period of time. This distribution
method gives users a chance to try software before buying it.
If the particular shareware application provides a service
which the user wishes to continue beyond the specified evaluation
period, a registration payment to the software author is required.

Copyright laws apply to both Shareware and commercial software,
and WinTECH Software retains all rights to its software products
with the following exception:

WinTECH Software specifically grants the right to copy and
distribute unregistered copies of the ModScan Application to all
interested parties for an evaluation period not to exceed thirty-days.

Advantages of Registration

The Shareware distribution system depends upon the integrity of
the user to make the required registration payment only if the
application proves itself useful.  Shareware products have the
ultimate money-back guarantee--if the product is not used, no
payment is required.  Registration of Shareware products support
this system of distribution and allow continued development of
low-cost high quality software solutions.

Registration of the ModScan Application

Unregistered copies of the ModScan Application are functionally
equivalent to registered copies with the following exception:

To encourage registration, a limit is placed on the amount of time
data may be collected during a monitoring session.  This limit
does not effect the ability of a user to fully evaluate either
the functionality or through-put of the application.  

Registration of the ModScan Application requires a registration
fee of $49.95 be submitted to WinTECH Software.  The user shall
receive in return the most recent registered version of ModScan
with all time limit constraints and registration reminder screens
disabled.   The user shall also receive a printed user manual,
and free technical support for a period of three months after
registration.  Registered users also have direct access to the
ModScan design engineer and a commitment from WinTECH to consider
product enhancements based on individual application requirements.
In other words, if you can think of anything which would make your
life easier, let us know.  If it has general marketing appeal,
chances are it could be included in the next revision.


Licensing Agreement

Registered WinTECH software is protected by both United States
Copyright Law and International Treaty provisions.  Therefore,
you must treat this software just like a book with the following
single exception.  WinTECH Software authorizes you to make
archival copies of the software for the sole purpose of backing-up
your software and protecting your investment from loss.

By saying "just like a book", WinTECH means for example that this
software may be used by any number of people and may be freely
moved from one computer location to another so long as there is
no possibility of it being used at two locations at the same time.
Execution of two copies of the same registered ModScan application
at the same time constitutes a Copyright violation and is expressly
prohibited.

Warranty

With respect to the physical diskette and physical documentation
enclosed herein, WinTECH Software warrants the same to be free of
defects in materials and workmanship for a period of 30 days
from the date of registration.  In the event of notification within
the warranty period of defects in material or workmanship, WinTECH
will replace the defective diskette or documentation.

WinTECH Software disclaims all other warranties, expressed or implied,
including without limitation, the warranties or merchantability
and of fitness for any purpose.  WinTECH Software assumes no
liability for damages, direct or consequential, which may result
from the use of this program.

ModScan System Requirements

Operational Overview

ModScan is a Windows application designed to operate as a master
communications device, polling one or more slave devices according
to the MODBUS protocol defined by Gould Modicon.  ModScan operates
using the standard Windows COM drivers and communicates using the
electrical protocol supported by the PC hardware.  Windows 3.1,
Windows for Workgroups  3.11, or Windows '95 is required.  At least
one free serial port is required.

ModScan was designed to operate as a simple one-on-one testing
application to verify proper slave response to standard MODBUS
query commands.  ModScan runs a single polling cycle, configurable
by the user, to access and display data points as required.  The
user may select any valid MODBUS slave address and range of data
points to scan.

System/Cabling Requirements

This manual assumes an RS-232  based communications system is to
be used to connect the ModScan application directly to a single
MODBUS slave device.  In this simple configuration, the cabling
requirements are defined by the RS-232 standard and the control
signals required by the particular slave device.  The application
supports RTS/CTS, and DSR/DCD/DTR operation, although these signals
are not required for ModScan operation.  If required by the slave
device, these signals may wired as shown in cable drawing 2.2.1
or jumpered out at the slave end of the cable as shown in
drawing 2.2.2. 

Installation

Making Backups

The distribution diskette is not copy-protected, and the registered
user may make backup copies as required.  The ModScan application
may be moved from one PC to another so long as the basic licensing
agreement of only one copy in use at a  time is maintained.  Site
licenses are available for commercial users by contacting WinTECH
Software.
	
Installing ModScan

Installation of the ModScan Application involves simply copying
the ModScan.exe & ModScan.hlp files from the distribution diskette
to a working directory on the hard disk.  After running the
application for the first time, a configuration file will be
created on the working directory.  ModScan.cfg represents the
user configurable selections, (slave address, data point type. etc.),
in effect at the time the program terminated. These settings will
be restored the next time ModScan is started.  

ModScan may be started from the program manager, file manager,
or program group icon.  Consult the Windows user's manual for
details.

Basic Operation

The MODBUS Protocol

The MODBUS protocol describes an industrial communications and
distributed control system developed by Gould-Modicon to integrate
PLC's, computers, terminals, and other monitoring, sensing, and
control devices.  MODBUS is a Master/Slave communications
protocol, whereby one device, (the Master), controls all serial
activity by selectively polling one or more slave devices.  The
protocol provides for one master device and up to 247 slave
devices on a common line.  Each device is assigned an address
to distinguish it from all other connected devices. 

Certain characteristics of the MODBUS protocol are fixed, such as
the frame format, frame sequences, handling of communications errors
and exception conditions, and the functions performed.

Other characteristics are user selectable.  These include a choice
of transmission mediasetup_serial, baud rate, character parity,
number of stop bits, and the transmission modes, (ASCII or RTU).
The user selected parameters are set, (hardwired or programmed),
at each station.  These parameters cannot be changed while the
system is running.

The mode of transmission is the structure of the individual units
of information within a message, and the numbering system used to
transmit the data.  Two modes of transmission are available for
use in a MODBUS system.  Both modes provide the same capabilities
for communicating with PLC slaves;  the mode is selected depending
on the equipment used as a MODBUS Master.  One mode must be used
per MODBUS system; mixing of modes is not allowed.  The modes
are ASCII (American Standard Code for Information Interchange),
and RTU, (Remote Terminal Unit.)

ASCII printable characters are easy to view when troubleshooting
and this mode is suited to computer masters programmed in a high
level language, such as FORTRAN, as well as PLC masters.  RTU
is suited to computer masters programmed in a machine language,
as well as PLC masters.

In the RTU mode, data is sent in 8-bit binary characters.  In
the ASCII mode, each RTU character is first divided into two 4-bit
parts, (high order and low order), and then represented by the
hexadecimal equivalent.  The ASCII characters representing the
hexadecimal characters are used to construct the message.  The
ASCII mode uses twice as many characters as the RTU mode, but
decoding handling the ASCII data is easier.  Additionally, in
the RTU mode, message characters must be transmitted in a
continuous stream.  In the ASCII mode, breaks of up to one
second can occur between characters to allow for a relatively
slower master.


Polling Operation

Only the master initiates a transaction.  Transactions are either
a query/response type, (only a single slave is address), or a
broadcast/no response type, (all slaves are addressed).  A
transaction comprises a single query and single response frame
or a single broadcast frame.

ASCII Framing

Framing in ASCII Transmission mode is accomplished by the use of
the unique colon, (:), character to indicate the beginning of frame
and carriage return/line feed, (CRLF), to delineate end of frame.
The line feed character also serves as a synchronizing character
which indicates that the transmitting station is ready to receive
an immediate reply.

RTU Framing

Frame synchronization can be maintained in RTU transmission mode
only by simulating a synchronous message.  The receiving device
monitors the elapsed time between receipt of characters.  If
three and one-half character times elapse without a new character
or completion of the frame, then the device flushes the frame
and assumes that the next byte received will be an address.

The address field immediately follows the beginning of frame and
consists of 8-bits, (RTU), or 2 characters, (ASCII).   These bits
indicate the user assigned address of the slave device that is to
receive the message sent by the attached master.

Each slave must be assigned a unique address and only the addressed
slave will respond to a query that contains its address.  When the
slave sends a response, the slave address informs the master which
slave is communicating.  In a broadcast message, an address of 0 is
used.  All slaves interpret this as an instruction to read and take
action on the message, but not to issue a response message.

Function Field

The Function Code field tells the addressed slave what function to
perform.  MODBUS function codes are specifically designed for
interacting with a PLC on the MODBUS industrial communications
system.  The high order bit in this field is set by the slave
device to indicate an exception condition in the response message.
If no exceptions exist, the high-order bit is maintained as zero in
the response message.

Data Field

The data field contains information needed by the slave to perform
the specific function or it contains data collected by the slave
in response to a query.  This information may be values, address
references, or limits.  For example, the function code tells the
slave to read a holding register, and the data field is needed to
indicate which register to start at and how many to read.  The
imbedded address and data information varies with the type and
capacity of the PLC associated with the slave.

Error Check Field

This field allows the master and slave devices to check a message
for errors in transmission.  Sometimes, because of electrical noise
or other interference, a message may be changed slightly while its
on its way from one device to another.  The error checking assures
that the slave or master does not react to messages that have
changed during transmission.  This increases the safety and the
efficiency of the MODBUS system.

The error check field uses a Longitudinal Redundancy Check, (LRC),
in the ASCII mode of transmission, and a CRC-16 check in the RTU mode.

Display Parameters

The display of the ModScan application consists of two parts.  The
top half of the display represents the addressing information which
specifies the remote slave device and data point type to scan.
Edit controls allow specification of the slave device identification,
point type, and point addressing information used for the scanning
operation.  These controls may be modified at any time, including an 
ctive scanning session.  Modification of these values during a 
scanning session will influence the next poll.

Immediately above the horizontal line separating the addressing data
from the actual data point display is a status line representing
current activity of the ModScan application.  During an active
polling session, this line will represent any  exception responses
received from the addressed slave or any communications errors which
may result from an invalid address specification or disconnected
serial line.

To the right of the display are two counters representing the number
of query messages attempted and the number of valid responses received.
During an active polling session, ModScan will attempt to poll the
specified slave device periodically depending on the poll cycle
selected.  These counters may be reset via a menu command and are
useful for picking up intermittent failures over an extended period
of time.

The bottom half of the display typically represents the results of
the most recent data scan.

If ModScan is configured to display MODBUS data points, Coil values
will be displayed as below.  ON status is displayed as '1', OFF as '0'.
ModScan will attempt to display all data points defined by the Length
parameter in the address specification using the available Window
display area.

Register values may be displayed in either Decimal or Hexadecimal
notation.  The address of each data point is followed by the contents
as shown below:  (Hexadecimal notation would include an 'H' after the
value such as 1000H.)

In order to write a MODBUS data point in a slave device, the
communications with the device must first be initiated by scanning
a series of data points by configuring the correct addressing
information and initiating a polling cycle.  Once the data is
successfully displayed on the screen, double-clicking the 
address/value portion of the screen will initiate a dialog box which
allows the value to be changed.  If the polling cycle has been
configured to represent coil addresses, double-clicking an address
will initiate the Change Coil Dialog:

The Change Register Dialog Box may be initiated by configuring the
display to represent register data and double clicking on an address:

Pressing the Update Button in either write data point dialog will
initiate the appropriate MODBUS write command, (05 or 06), during
the next scheduled poll.

Menu Selections

Setup

The SetUp Serial menu command allows the user to control the
physical characteristics of the MODBUS connection.  The PC COM port
to use may be selected, as well as the baud rate, number of stop bits,
and parity.  The RTU transmission mode dictates that 8 data bits
are used while the ASCII mode of transmission allows either 7 or 8
data bits to be used, (even though the eighth bit is not used).

The RS-232 handshaking lines may be configured by checking the
appropriate boxes depending on the characteristics required by
the connected slave device.  
The Setup Protocol Menu commands allow the user to specify either
RTU or ASCII transmission modes.  The transmission mode may not be
changed while an active session is in progress.  The polling cycle
must be stopped before these menu options are activated.

The polling cycle and associated message time-out are also
configurable via the Setup Protocol Menu Commands.  The polling
cycle represents the time delay between successive polls and is
specified in seconds:

The message time-out determines how long the ModScan application
waits for a response from an addressed slave device and is specified
in milliseconds:

These menu commands initiate or stop a ModScan polling cycle.  The
Start Polling Menu command begins a repetitive cycle of polling
the slave device specified in the addressing section of the display.
The device to poll and the point type and addressing parameters may
be changed at any time during a polling cycle.  As data is received
from the slave device, it is displayed in the data point section
of the screen.  The Stop Polling Menu selection simply halts the
polling process and returns the ModScan application to an Idle condition.

Display Options

The SetUp Display Menu consists of four line items representing
two mutually exclusive options.  The display may be configured to
display data points or serial traffic by clicking on the appropriate
menu selection.  The option in effect is represented by a check mark.
Likewise, register data may be displayed in either decimal or
hexadecimal notation depending on the menu item selected.  To
change from one notation to the other, simply click the unchecked
option.

Monitoring Serial Data

In certain cases, it may be desirable to monitor the actual MODBUS
communications between the ModScan application and a particular
slave device.  The application allows the serial data traffic to
be displayed to the screen as it occurs by selecting the View
Traffic option under the Setup DisplayMenu Command options.  If
enabled, the bottom portion of the ModScan display will depict
all serial data characters transmitted and received as they occur.
Transmitted characters are displayed in reverse video, received
characters are displayed in normal video.  Display of the actual
serial traffic is sometimes useful for troubleshooting an
intermittent communications fault or debugging a new design.

Technical Support

Contacting WinTECH

If it ever becomes necessary to contact WinTECH concerning a
technical question or to offer comments or suggestions for
improving the Listen application please call or write to the 
ddress below:

	WinTECH Software
	P.O.Box 907
	Lewisburg, WV  24901

	(304) 645-5966


For quickest response, email questions/comments to:

modscan@win-tech.com