ModLink

Change Log

2.20 (February 26, 2010)

New: ModLink has undergone thorough testing and is now officially certified to be Windows 7/Vista compatible.
New: Serial communication subsystem has got a bit of overhaul that improves performance and overall stability especially under stressed conditions.
Fix: Reception of a corrupted response frame in Modbus/RTU transmission mode gets sometimes misinterpreted as if no response was received at all (response timeout expired).
Fix: Reception of a corrupted request/response frame in Modbus/ASCII transmission mode results in EAssertionFailed to be thrown with message 'DecodeFrame: Trailing CR is missing'.
Fix: ReceiveTimeout property of TModbusConnection is misused to govern the entire process of reception of Modbus data frames. As a result, they are being truncated prematurely if ReceiveTimeout is smaller than the time required to transmit the entire frame over the network.
Various tweaks.

2.13 (September 21, 2009)

New: Added support for Embarcadero Delphi 2010, C++ Builder 2010 and RAD Studio 2010.
Fix: Attempting to assign TModbusConnection->Port property programatically in C++ Builder code results in [Linker Error] Unresolved external '__fastcall Modlink::TModbusConnection::SetPortA(System::AnsiString)' referenced from ...

2.12 (March 8, 2009)

New: Added support for CodeGear Delphi 2009, C++ Builder 2009 and RAD Studio 2009.

2.11 (May 14, 2008)

New: Added support for CodeGear C++ Builder 2007.
New: Added support for Delphi for Win32 and C++ Builder personalities of CodeGear RAD Studio 2007.
New: When using RTS-Toggle flow control, TModbusConnection component now allows for an arbitrary time gap (adjustable via RTSHoldDelay property) to be inserted before the RTS line gets lowered to logical zero after the buffered data waiting for transmission have been sent. This apparently leads to a better compatibility with certain RS-232<->RS-485 converters.
New: TModbusConnection component is now able to notify the application about reception of corrupt/incomplete Modbus data frames via OnInvalidFrameDiscard event. This event occurs whenever the incoming request from remote Modbus client does not pass an error check to ensure its data integrity.
New: TModbusServer component is now able to notify the application about the actual reason of its inability to handle a specific Modbus client request via OnCommandHandlerException event. This event occurs whenever an exception gets raised while the incoming request from remote Modbus client is being handled.
Change: Replaced the Windows automatic RTS-Toggle flow control implementation with a custom one due to (i) tendency of lowering the RTS line to logical zero too early even before the buffered data waiting for transmission actually had a chance to be sent to the wire, and (ii) inability to work at all under Windows 95/98/ME.
Fix: There were some issues related to communication with a certain combinations of Modbus server devices and signal converters.
A couple of internal tweaks.
Updated the documentation.
Added three new example projects that demonstrate how to write a basic Modbus client/server applications using ModLink.

2.10 (June 03, 2007)

New: Added support for CodeGear Delphi 2007 for Win32.
New: TModbusConnection component now makes it easy to intercept a moment whenever data frame is about to be sent to the serial network and provide additional behavior via newly introduced OnBeforeFrameSendAsync and OnAfterFrameSendAsync events. As indicated by 'Async' suffix both of them get triggered within the context of internal transaction management thread.
Improved: RTS and DTR serial line signals can now be set manually during the communication session in order to allow for customized data flow control.
Fixed: Attempting to initiate client requests at a very high rate may result in some responses from remote server to be lost.
Fixed: Reception of zero sized data frame may result in either ERangeError or EAccessViolation to be raised, depending on whether range checking option is enabled or not.
A couple of internal tweaks.
Updated the documentation.

2.9 (December 20, 2006)

New: Extended TServerReply enumerated type with srUnexpectedReply member. This value indicates reception of response data frame that was originated by "unexpected" remote server. Such change was introduced to allow for better granularity when distinguishing between a response from "unexpected" server and an unmatched response from "expected" server.
Change: Upon reception of response from "unexpected" remote server, the active Modbus transaction is now kept waiting for another response (hopefully) from "expected" remote server while global response/receive timeout is still in action. Previously there was no such implicit retry and the active Modbus transaction was marked as unmatched in this case.
New: TModbusClient now provides a centralized way to notify application about every processed Modbus transaction via single OnTransactionProcessed event. Component developers are advised to override protected DoTransactionProcessed method instead.
New:Added mechanism which allows TModbusClient to keep track of number of consecutive Modbus transactions that timed out (i.e. those transactions where either none or unexpected response was received from remote server within given timeout). As soon as internal counter exceeds the limit imposed by MaxConsecutiveTimeouts property, application will be notified via OnConsecutiveTimeoutLimitExceed event. Provided that MaxConsecutiveTimeouts property is set to a reasonable value, this mechanism might be useful to determine whether or not the remote server is still responding during the communication session. Component developers are advised to override protected ConsecutiveTimeoutLimitExceed method instead.
New: TModbusConnection now allows for size of internal reception/transmission serial device buffers to be adjusted as needed via newly exposed InputBufferSize and OutputBufferSize properties which both default to 1024 bytes.
A couple of internal tweaks.

2.8 (July 20, 2006)

New: Added support for public Modbus command Read/Write Multiple Registers (code $17). This command can be used to perform a combination of one read operation and one write operation in a single Modbus transaction. It has the same effect as if both Write Multiple Registers and Read Holding Registers commands were called successively (in that order), but generally it takes much less time to complete.
New: Extended TServerReply enumerated type with a new srInvalidFrame member. As the name says, this member is intended to indicate that a partial, incomplete or otherwise corrupted Modbus data frame (response) has been received from a remote Modbus server.
Change: ServerAddress property of TModbusClient component may now be changed at any time, again (reconsidered the restriction imposed in previous release). There is one difference, though. If the property value is being changed while TModbusClient is associated with an active TModbusConnection instance, all pending Modbus transactions originated by that TModbusClient will be immediately discarded upon the change.
Fix: Upon reception of unmatched server response (i.e. Modbus data frame whose server address and/or command code fields do not match their counterparts in the original client request), TModbusConnection component will no longer discard the current transaction results, and immediately make another attempt to receive even more data from a remote Modbus server, apparently without having any chance to succeed.
A couple of internal tweaks.
New: Demo application now provides necessary infrastructure required for management of transactions based on the newly implemented public Modbus command Read/Write Multiple Registers (code $17).
New: Demo application now supports optional logging of various activitity to a disk file. This covers complete Modbus transaction management (client-side and server-side) including all incoming/outgoing traffic over the serial network.
Updated the documentation.

2.7 (March 09, 2006)

New: Added support for Borland Developer Studio 2006. For this version of IDE, ModLink components come in form of dual/shared packages which means once installed, they will be accessible from both Delphi 2006 for Win32 and C++ Builder 2006 for Win32 personality as well.
New: TModbusClient component is now able to initiate custom Modbus transactions based on user-supplied command code and data. Once entered, ModLink will then take a care of generating the protocol header, appropriate error check field, wrapping them up along with the raw request data into valid Modbus frame, and forwarding it to the transaction engine for further processing. This feature is especially useful when there is a need to interface with certain devices that implement proprietary device-specific commands not defined in the standard Modbus specification.
New: During the processing of remote Modbus client request by TModbusServer component, the application is now able to abort the action that is currently being performed and specify which kind of Modbus exception response is to be transmitted back to a remote Modbus client (instead of a normal Modbus response).
New: The contents of server item listview in the demo application now persists between the sessions.
Fix: OnFrameReceive event of TModbusConnection component will no longer be triggered upon receipt of zero bytes (i.e. whenever the receive operation of underlying serial transport times out).
Fix: ServerAddress property of TModbusClient component is no longer allowed to be modified while TModbusClient is associated with an active TModbusConnection instance. Additionally, there are no restrictions imposed upon the value of this property anymore.
Fix: Should TModbusServer component fail to perform an action indicated by remote Modbus client request (particularly due to a runtime exception being raised from within a server command handler), a special Modbus exception response with code $04 (SERVER_DEVICE_FAILURE) is now guaranteed to be transmitted back to a remote Modbus client. Previously, no response was sent by TModbusServer component at all in such cases.
Fix: When running in a Modbus server mode, the demo application will no longer cause EAccessViolation exceptions to be raised whenever an item gets removed from the server item listview.
Updated the documentation.

2.6 (August 23, 2005)

TModbusConnection component is now able to optionally hook already opened serial port rather than explicitely open one for exclusive access. This feature may be useful in cases when handle to the same serial port has to be shared between multiple parties (e.g. in addition to ModLink, you may want to use a third-party TAPI library to establish/drop a connection with external modem device). Hooking already opened serial port is as easy as setting the value of HookExistingPort property to True and providing a handler for OnGetHookedPortHandle event that gets triggered during the activation sequence.
Fix: In the {$R+} state when generation of range-checking code is enabled, TModbusConnection component no longer causes ERangeError or EAccessViolation (in earlier versions of Delphi) runtime exceptions to be raised whenever empty response frame is received from a remote Modbus server.
Fix: When the value of EchoQueryBeforeReply property is True, TModbusConnection component no longer triggers OnFrameReceive event upon reception of Modbus query frame echoed back by certain RS-232 <-> RS-485 converters.
User settings in the demo application now persist between the sessions.
Fixed a couple of minor bugs in the demo application.
Updated the documentation.

2.5 (May 16, 2005)

Added support for new Modbus command: Read Exception Status (code $07). This command can be used to read the contents of eight exception status outputs in a remote Modbus server.
Added support for new Modbus command: Report Server ID (code $11). This command can be used to read the description of the type, the current status, and other information specific to a remote Modbus server.
Fix: Finally managed to remove annoying TModbusClient/TModbusConnection shutdown bug which caused a runtime exception to be raised during dispatching of pending Modbus transactions when either or both these components were about to be destroyed.
Increased scope visibility (from private to protected) of relevant TModbusConnection methods (WaitForData, ExamineInputBuffer, InternalReceiveFrame, and SendFrame) in order to let application developer to perform custom data interchange over the serial line as well (e.g. to establish or drop a connection with external modem device).
A couple of internal tweaks.
Updated the documentation.
Updated the demo application.

2.4 (January 24, 2005)

Added support for Borland Delphi 2005 (Win32 Personality only).
Introduced new EchoQueryBeforeReply property in TModbusConnection. This property allows ModLink based applications to take care of RS-232 <-> RS-485 converters that automatically echo the data frame (Modbus query) immediately after its reception back to the client that originated the transaction.
Fix: Under certain circumstances, TModbusClient could raise a runtime exception during TModbusConnection shutdown when there were some pending Modbus transactions in the transaction queue. This is no longer possible.
Improved the layout of TModbusConnectionEditForm dialog.
Updated the documentation.
Updated the demo application.

2.2 (December 22, 2003)

Implemented support for the five additional Modbus commands in the server simulation mode: Read Coils (code $01), Read Discrete Inputs (code $02), Write Single Coil (code $05), Write Single Register (code $06), and Write Multiple Coils (code $0F).
Fix: Added a workaround the delayed serial port driver notification issue that occurs in the Windows OS family. Due to this issue, an incomplete Modbus frames were received by TModbusConnection under some circumstances, if the value of RealSilentInterval property was less than approx. 20 milliseconds. From now, the value of the real silent interval is forced to be at least 20 milliseconds.
Fix: TModbusConnection now allows for the DTR and RTS lines of the serial port to be enabled/disabled and left on/off during the communication session provided that they are not used in any kind of the hardware data flow control mechanism. In the previous versions those lines were always disabled and left off by default (in case of no hardware data flow control mechanism), which caused several remote Modbus servers to fail to respond. For this purpose, a new DTREnabled and RTSEnabled properties have been introduced.
Introduced new DiscardPendingTransactions method in TModbusConnection. As the name says, this method is intended to discard all pending transactions in the internally maintained transaction queue. However, it is possible to restrict the removal process only to those pending transactions that were previously initiated by given TModbusClient.
Added a set of routines intended for a bidirectional conversion between a real world values that occupy multiple Modbus registers, and a Modbus register's native storage format compliant values. They are: LongInt2Mod, Mod2LongInt, LongWord2Int, Mod2LongWord, Single2Mod, Mod2Single, Double2Mod, and Mod2Double. Those already existing routines that operate with a real world values that occupy only a single Modbus register were just renamed:
- Float2Mod -> ScaledFloat2Mod,
- Mod2Float -> Mod2ScaledFloat,
- Int2Mod -> SmallInt2Mod,
- Mod2Int -> Mod2SmallInt.
Introduced new ExceptionCodeToStr method in TModbusConnection. As the name says, this method is intended to convert the Modbus exception code acquired by the client from the reply returned by a remote server into a meaningful description. The method first fills the result string with a default description and then it lets the application to adjust this default description by triggering a newly introduced OnTranslateExceptionCode event.
Fix: Fixed the bug in the internal window procedure of TModbusConnection which was causing the application using ModLink components not to respond properly to WM_QUERYENDSESSION message, thereby preventing the Windows system to be shut down. Thanks to Vadim Tishkevich for the bug report/fix.
Source code restructure and internal tweaks.
Updated the documentation.
Updated the demo application.

2.1 (May 20, 2003)

Private release. Added preliminary (experimental) support for local Modbus server simulation in ModLink.
Introduced new component: TModbusServer. This component is intended to simulate a local Modbus server which listens on the serial port for incoming Modbus transactions initiated by a remote Modbus client and performs the action requested in the query. Currently, only three Modbus commands are supported: Read Holding Registers (code $03), Read Input Registers (code $04), and Write Multiple Registers (code $10).
Introduced new ConnectionMode property in TModbusConnection. This property is used to determine in which mode (either a local client mode or a local server mode) will TModbusConnection operate, when activated. Since this version, TModbusConnection may be shared with both TModbusClient and TModbusServer components as well, however it's designed to operate only with the objects of one kind upon activation.
Source code restructure and internal tweaks.

2.0 (May 12, 2003)

Rewritten and optimized nearly every line of code for serial communication and Modbus transaction management to comply with the new Modbus specifications.
Removed the dependency on ComPort Library. From now, ModLink doesn't require/rely on any third-party VCL extensions, external DLLs or OCXs.
Added support for five additional Modbus commands: Read Coils (code $01), Read Discrete Inputs (code $02), Write Single Coil (code $05), Diagnostics (code $08, all sub-codes), and Write Multiple Coils (code $0F).
Added support for Modbus/ASCII serial transmission mode.
Made it possible to initiate broadcast Modbus queries as well. A new TurnaroundDelay property was introduced in TModbusConnection which is now able to insert a specific delay after sending the Modbus broadcast query in order to allow any remote server to process the current query before sending a new one.
Introduced two new events in TModbusConnection: Using OnReceiveFrame and OnSendFrame events it's very easy to monitor the serial network and examine all incoming/outgoing raw data frames from/to a remote Modbus servers.
During the initiation phase, every Modbus transaction now gets assigned an unique ID to help application developers keep track of particular Modbus transaction.
Added support for Borland Delphi 4 development environment.
Added a lot of useful design-time enhancements to the Delphi IDE, such as introducing of property categories, and various property/component editors.
Updated the documentation.
Source code restructure and internal tweaks. Unfortunately, there were so many significant changes to the source code, so the backward compatibility with previous versions of ModLink has been broken.

1.3 (December 10, 2002)

Corrected the typo in the source code: ftTimeout member of TFailReason renamed to frTimeout.
Added support for two additional Modbus commands: Read File Record (code $14), and Write File Record (code $15).
Fix: Imposed additional restrictions upon input parameters in ReadHoldingRegisters, ReadInputRegisters, and WriteMultipleRegisters methods of TModbusClient. These methods now make sure that no item of range of register references to be read/written exceeds the upper Word ($FFFF) boundary.
Stripped RegCount parameter out of WriteMultipleRegisters method of TModbusClient for redundancy reason (this information can be retrieved indirectly from the supplied array of register values). This action caused the backward compatibility to be broken.
Introduced new CountPendingTransactions method in TModbusConnection. As the name says, this method is intended to retrieve information about the total item count in the internally maintained pending transaction list. However, it is possible to restrict the list search only to those pending transactions that were previously initiated by given TModbusClient.
Added an ability to associate any Modbus transaction with the pointer to user-defined data. This pointer may be supplied via an optional parameter of any of the transaction initiation methods defined in TModbusClient. Similarly, it may be retrieved at a later time, when the particular transaction has been completed.
Added support for Borland Delphi 7 development environment.
Updated the documentation.
Source code restructure and internal tweaks.

1.2 (October 6, 2002)

Introduced several changes in the interface part of the main unit in order to increase the source code consistency. As a result of this action, the backward compatibility was broken, so existing code which uses ModLink must be slightly adjusted to be up-to-date:
- TSingleRegisterPresetEvent event prototype renamed to TSingleRegisterWriteEvent.
- OnSingleRegisterPreset property of TModbusClient renamed to OnSingleRegisterWrite.
- PresetSingleRegister method of TModbusClient renamed to WriteSingleRegister.
- TModbusRegistersReadEvent event prototype renamed to TMultipleRegistersAccessEvent.
- seIllegalFunction member of TSlaveException renamed to seIllegalCommand.
- seSlaveDeviceException member of TSlaveException renamed to seSlaveDeviceFailure.
- RegValues value parameter of TMultipleRegistersAccessEvent changed to a constant parameter.
- Analysis value parameter used in TMultipleRegistersAccessEvent, TSingleRegisterWriteEvent, and TLoopbackTestExecuteEvent changed to a constant parameter.
Added support for two additional Modbus commands: Write Multiple Registers (code $10), and Mask Write Register (code $16).
Added a set of utility routines intended for conversion from a real world values to a Modbus register's native storage format and vice versa. They are: Float2Mod, Mod2Float, Int2Mod, and Mod2Int.
The scheduling priority of the background transaction management thread can now be adjusted via new TransactionThreadPriority property of TModbusConnection.
Improved a Modbus transaction analysis which is now a bit faster.
Fix: Imposed additional restrictions upon input parameters in ReadHoldingRegisters and ReadInputRegisters methods of TModbusClient.
Added a sample application demonstrating the key features of ModLink. Full project sources (compatible with Borland Delphi 5/6) are included.
Updated and clarified the documentation.
Internal tweaks.

1.1 (August 17, 2002)

Massively updated the documentation which is almost complete now.

1.0 (August 9, 2002)

First public release.
Built-in support for Borland Delphi 5/6 development environments.
Included preliminary HTML Help documentation in a compiled form.