Totally Accurate Clock (32-bit)
for Windows 95, 98, NT 4.0, and XP

Release Notes for Version 1.0 to 1.2.8


Version 1.2.8, August 9, 1998

Features: Implemented a new Manual GPS Receiver Commands dialog box under the Data menu. This allows the expert user to send any command to the GPS receiver. This is especially useful to activate and deactivate messages to support custom applications.

Reference locations may now be saved in a user-specific data base with user-defined names by using the Manual Reference Location dialog box. The GPS receiver can be loaded with data from this data base or data base entries may be added and removed without interfering with the operation of the GPS receiver. Refer to Help or the program documentation for details and cautions before using this new feature.

The position and size of all dialog boxes and view port screens are now saved so they will appear the same the next time the program is run.

All log types can now be conditioned to record data every "n" seconds.

Updates: Updated help files and documentation. The full documentation is now available on the Web as an Adobe file. The documentation has had significant structural and content updates so those who had the previous documentation in either printed or electronic form should replace that documentation with this new document.

Improved the handling of special case situations such as operation without a one-pulse-per-second signal, loss of GPS receiver lock, and loss of critical GPS receiver messages.

Added LMR-240 and LMR-400 coax types to the coax calculators.

Garmin receivers operating in  NMEA mode now have the $PGRME message activated for compatibility with other software programs.

Corrections: Corrected a number of minor bugs in the logging functions including one that cause a program crash under certain circumstances.

Corrected the parsing algorithm for the latitude and longitude fields in the Manual Reference Position dialog box so that "E", "W", "N", and "S" designators can now be used in lieu of "+" and "-".


Version 1.2.7, June 8, 1998

Corrections: Corrected an initialization error for Motorola receivers that caused cold start and restart (when not locked onto satellites) to take much longer than necessary.

Improved receiver type detection algorithm.

Redesigned the satellite visibility screen to eliminate problems with coordinate labels and simplify the grid. Also corrected the Help file to match these changes and the changes made in version 1.2.6.

Satellite data is now displayed during receiver startup modes, including ephemeris acquisition.

The DGPS reception status messages now work correctly for receivers without 1PPS.


Version 1.2.6, May 9, 1998

Performance: Reduced CPU loading by about 10 percent.

Corrections: Corrected an error in the algorithm used to probe for serial ports. This error caused some ports to fail to be detected and could have caused the program to fail to initialize correctly on some platforms.

Changed the default averaging limits to 1/3 day for position and timing, 1 day for RMS averaging.

Refined the averaging algorithms to eliminate errors that occurred in various specific conditions. This will improve position averaging in NMEA mode and correct errors in the time accuracy estimate values.


Version 1.2.5, May 5, 1998

Corrections: Corrected a timing error that caused the UTC display and PC time setting, if enabled, to be one second behind true UTC if the combination of Epoch Offset and Intentional Extra Early Offset produced a Total 1PPS Offset From UTC between 999.5 and 999.999999 msec (same as -0.5 to -0.000001 msec).

Improved the efficiency of the initialization and re-initialization process. Tac32 now starts up quicker and responds very quickly to changes in its configuration parameters.


Version 1.2.4, May 2, 1998

Features: Changed the satellite colors on the Az-El graph to Blue for rising (approaching), Red for setting (departing) and Cyan for Unknown. This reflects the astronomer's bias towards describing these states in terms of "red-blue shift" rather than the engineer's bias towards "good-bad" (green-red).

Added signal strength (Eb/No) to the pop-up windows on the satellite Az-El chart.

Corrections: Improved the operation of the "Probe for New Ports" button in the "Serial Port Settings" dialog box.

Revised the "Receiver not found" warning box to have only one button, "OK".

Changed a label on the main screen from "GPS Time" to UTC Time from GPS" to be more precise.

Corrected an error interpreting and displaying the station ID in the DGPS being received message.

Revised the initialization for Garmin receivers.  Some receivers seem to play by a different set of rules, like the GPS-III.


Version 1.2.3, April 28, 1998

Features: There is a new Satellite Azimuth / Elevation (visibility) polar plot chart (View / View Satellite Az-El Chart) that provides a visual status of satellite location and movement. Place the cursor over a satellite icon to see details. The satellite icons are color coded - green for rising, red for setting and blue for unknown.

The toolbar has been redesigned to enhance ease of use.

Performance: Probing for the existence of serial ports is now done only once and the results are stored. This speeds up subsequent program initialization.  If you change your serial port hardware configuration use the new Probe for Serial Ports button in the Edit/Set Serial Port dialog box.

When Tac32 fails to find an active GPS receiver on the selected serial port it will stop issuing initialization commands and will display an instructive message to the user.

Corrections: Position averaging now suspends height averaging during periods of 2-D navigation.

Corrected an error that would cause Tac32's communication thread to lock up if another program had initialized the GPS receiver to send @@Bl commands.

Corrected an error that would cause Tac32 to crash if certain illegal data was detected in the NMEA $GPZDA or $GPRMC messages. This happens whenever a Motorola Oncore GT+ looses satellite lock (like when the antenna is disconnected). It does not occur with the Motorola Oncore VP or Garmin receivers.

Eliminated a problem where the PC clock would get set twice every second to slightly different values if the NMEA message set took almost exactly one second to send.

Corrected a problem with the satellite data display when using a Motorola Oncore GT+ receiver in NMEA mode (works differently than the Oncore VP).

When switching from a Motorola Oncore VP to a Motorola GT+ by resetting using the serial port dialog but not restarting Tac32, when both are in NMEA mode, now results in the correct setup parameters being applied. For example, if the VP was in 0-D navigation mode, the GT+ will be placed in 2-D mode (it has no 0-D mode).

Help Files: Updated the help files to reflect these changes.


Version 1.2.2, April 14, 1998

Motorola Oncore UT, UT+, GT and GT+ receivers: Tac32 now fully supports the Motorola Oncore UT, UT+, GT and GT+ receivers (as well as the VP and 6-Pack receivers and various Garmins).

Corrected the Eb/No readings for Motorola GT/UT series receivers in both binary and NMEA modes. Motorola changed the rules on how these fields are coded compared to the VP.

The receiver type is now reported in NMEA mode as well as binary mode.

Refined the default setup parameter display for the Motorola UT/GT series receivers.

Features: Receiver Setup Screen: Separated the "Timing or DGPS" button into "Precision Timing" and "DGPS Output" buttons with slightly different parameter settings. The "DGPS Output" button is only enabled for receivers with this capability.

Manual Reference Location setup screen: Simplified the screen by eliminating the four altitude calculator buttons. Changing either Altitude(MSL) or Altitude(WGS84) will cause the other value to be updated automatically (see bugs, below).

Bugs: Corrected an error in calculating the geoid-ellipsoid offset. Tac32 now calculates altitude values exactly the same way as most GPS receivers, producing the same results.

All Motorola receivers are now initialized to zero GMT offset.

Initialization is now more intelligent so that when a different receiver type is connected that is not compatible with the previous settings Tac32 reverts to "search" mode automatically. This is true both on startup and when using the serial port setup screen to reinitialize.

Help Files: Updated the help files to reflect these changes and corrected some typographical errors.


Version 1.2.1, April 12, 1998

Motorola Oncore UT, UT+, GT and GT+ receivers: Tac32 now fully supports the Motorola Oncore UT, UT+, GT and GT+ receivers (as well as the VP and 6-Pack receivers). The receiver status line now identifies the type of Motorola receiver detected.

The GT/UT series receivers do not report Mean Sea Level (they always report 0.00 feet) so Tac32 substitutes its own internal calculation for MSL. This calculation is not as accurate as that included in the Oncore VP but should be within ½ meter or so between +-80 degrees latitude.

The GT/UT series receivers do not report the full set of DOP values in binary mode so the DOP weighting algorithm is disabled in the averaging algorithm.

Only the Motorola Oncore VP supports the full set of features available on the various setup screens. Unsupported features are represented by disabled controls. The setup screens now show the correct default values for all disabled controls, based on receiver type and mode.

Performance: Improved program efficiency, reducing CPU load by over 20%.

Display: TheDGPS Status message now displays correctly. The satellite status display format is improved by incorporating the message lines into the underlying grid and placing the DOP messages on a separate line.

Bugs: Corrected a program failure that occurred when there were more than 12 satellites in view. This actually occurred for a few brief moments here when I had the elevation mask set to 0 degrees.

The Timing window now correctly restores all its values the previous state on Cancel.

Corrected an error in calculating the time zone offset value that caused the PC-U display to show incorrect values and caused the PC Clock to be reset every second when clock reset was based on clock error. This showed up after the switch to Daylight Savings Time.


Version 1.2.0, March 13, 1998

This release marks the end of the Beta phase of Tac32's development. As of this date Tac32 is now an official product.

Initialization: Tac32 now shows the main window immediately on startup. The status bar displays information on the progress of the initialization process, while the clock display shows "Initializing..."

Help: Added a new section called "How to Synchronize Other Windows 95, 98 and NT Computers to This One..." This section describes the use of the Net Time command.

GPS Receiver Setup: Changed the names of the default settings buttons from "Nav" and Timing" to "Navigation" and "Timing or DGPS" respectively. Changed the operation of the "Timing or DGPS" button to select Highest-in-Sky geometry for Motorola receivers and 2-D Nav for Garmin receivers.

Beta Releases


Version 1.1.11, Mar 4, 1998
  • Performance Enhancement: Reduced memory and resource requirements, improved execution speed and responsiveness. Added dynamic throttling (internal flow control) and smart screen control. The results are impressive! Tac32 now uses about half the CPU cycles with no loss in functionality. When executed on a slow or overloaded computer, Tac32 is now friendly and cooperative. I now have Tac32 running on a 486/66 with 8 Mb RAM and Win95b. Performance on this machine is not stellar but it works.
  • Windows 98 (Beta 3): Version 1.1.10 didn't work on Windows 98 but this one does.
  • Logging: Tac32 now remembers and uses the last directory accessed by File New or Open between program sessions. This makes it easier for you to return to a special directory where you keep logs.
  • Format: Redesigned the main screen to give it a cleaner look and to reduce its width. This allows the screen to fit better on an 800x600 screen with small fonts. It also allows a close but useful fit for 800x600 large font and 600x480 small font screens. Corrected a spelling error in the title bar of the "Set PC Clock" window.
  • Data: Changed the SNR to Eb/No scaling factor for Garmin receivers from 20db to 17db (10log10(50Hz)). It seems that the 20db used by ShowTime is wrong. Now Garmin and Motorola receivers show nearly identical results when connected to the same antenna at the same time.
  • Sound: Added a new choice, normal ticks only.  This selection is for the casual user, especially for Garmin users, who do not like or need the unlock sound.


Version 1.1.10, Feb 19, 1998
  • Default buttons on the Receiver Mode Screen no longer cause unexpected changes to the DGPS settings.
  • An informative message is now displayed below the satellite data on the main screen when DGPS signals are being received. his works for both NMEA (Motorola or Garmin) mode with SC104 messages and Motorola Binary mode with proprietary Motorola DGPS messages.
  • The satellite rise/set indicators now appear immediately for Motorola receivers (both NMEA and Binary modes).
  • System time set and Out of lock indicator changes:
    • Error reporting on system time set failure is enhanced to provide a more informative message.
    • Tac32 is now prevented from making any attempt at setting the system clock when it detects an out of lock condition.
    • Improved the handling and reporting of out of lock warnings for unusual cases.
  • Added support for the Garmin GPS-25LP receiver. See the "How to ..." Help topic for important information.
  • Corrected the default main window size for first time users.


Version 1.1.9, Feb 8, 1998: This is a bug fix release.
  • Rereads the receiver ID message when the serial port is reset to allow hot switching of receivers without shutting down Tac32.
  • Altitude averaging is now correctly calculated for Garmin receivers.
  • Added a user selection to the Averaging Parameters window to enable or disable reset of the averaging process on recovery from an unlock condition. This Garmin users should disable this reset in order to get good long term averaging results as they seem to loose lock quite often.
  • Revised the way satellite status data is generated, sorted and displayed to improve responsiveness and show up to 12 satellites in Motorola Binary mode.
  • Eliminated reporting of invalid DOP values on the satellite status display. This primarily effected 2-D and 0-D (timing) navigation modes.


Version 1.1.8, Jan 24, 1998: This is primarily a bug fix release.

New Features

  • Implemented choice of logging frequency to support long term PVT data collection studies. See New Log File and Open Log file Help for more information.

Bug Fixes:

  • Changed the method used to locate installed serial ports to prevent lockup of a serial mouse and DOS programs using a serial port.
  • Improved the shutdown sequence to prevent a rare shutdown error.
  • The receiver status on the Status Bar now correctly shown Motorola Binary mode.
  • Changed the heartbeat monitor display to reduce CPU loading and make it more esthetically pleasing.
  • File New, Open, Save and Close menu items are now correctly enabled and disabled for PVT logs.
  • Made a number of internal changes to improve performance and reduce memory utilization.


Version 1.1.7, Jan 18, 1998: This is a bug fix release.
  • Dynamically size the receiver status frame in the status bar so the longest message fits regardless of the system font size in use.
  • Allow the left frame of the status bar to shrink to zero when the main frame is made smaller (e.g., to show only the clock) so the more important status bar frames will stay visible.
  • Added line break at the end of the spread sheet header line (line two) in the PVT log.
  • Corrected a spelling error in the NMEA PVT log header.
  • Made the clock red and properly update the PC time for receivers without 1 PPS, including Motorola Oncores with 1 PPS disabled by T-RAIM.
  • Timing dialog data now saved correctly.
  • Added a PC Clock Sync counter to the Set PC Clock window (see Help for more information).
  • Added Motorola firmware revision number to the status bar.
  • Improved the reliability of Motorola NMEA results by ensuring a valid version number has been received before switching to NMEA mode.
  • Improved thread shutdown code to eliminate a rare error on program termination.


Version 1.1.6, Jan 17, 1998: This version includes all of the outstanding suggestions and bug fixes that have been received from the beta testers.

New Features:

  • Tac32 no longer stops reporting data when 1 PPS timing mark signal is halted by T-RAIM. This also allows GPS receivers without the 1 PPS signal to use Tac32 to display data.
  • DGPS output commands are now implemented on the GPS Receiver Mode Selection screen. At present Tac32 does not process the resulting data but this feature allows users to set up Motorola receivers that have DGPS output capability (binary mode only). This feature is primarily for use by the DGPS development team.
  • The satellite elevation column now includes up and down arrows to indicate rise and set trend.
  • Added a new user interface for setting the PC Clock synchronization method. Added a new synchronization method that allows the PC clock to be re-synchronized when the PC Clock drifts beyond a user selectable number of milliseconds. Added "Time of Last Sync" window to the new "Set PC Clock" window.
  • Improved the reliability of detecting 6-channel vs. 8-channel Motorola receivers by dynamic testing rather than relying on firmware revision level.  This allows 6-channel receivers that have had firmware upgrades to work correctly.
  • Dynamically detect DGPS and T-RAIM capability.
  • The main window status bar now shows more information about Motorola receivers (mode, number of channels, and whether T-RAIM and/or DGPS options are available).
  • Began the implementation of custom log types.  Added a log type selector window to the New and Open commands. Added a new log type, "Time, Position, Velocity, Etc.", to log PVT data in a spread sheet friendly format. See Help for New and Open commands for more information.

Bug Fixes:

  • Timing parameters are now set up correctly on program start up.
  • The "Locked Since" time is now set correctly.
  • Corrected an error that sometimes prevented all the satellites from being shown when the satellite list was not sorted (no sort buttons depressed) in the Motorola binary mode.
  • Corrected log time stamps for New, Open, and Save headers.


Version 1.1.5, Jan 2, 1998: This is a bug fix release.

Major revisions:

  • Properly accumulates list of previously active satellites for display on the Satellite Activation Grid.
  • Made the rendering of the satellite data and bar graph grid dynamic to prevent distortion due to changing the system default font (e.g., selecting Large or Other fonts).
  • Changed the method for determining the system time zone setting to solve an incompatibility with international versions of Windows.
  • Corrected a startup error setting the T-RAIM parameters.
  • Updated the algorithms for calculating Modified Julian Date and GPS Week.

Minor revisions:

  • Revised the layout of the GPS Receiver Mode Selections Dialog.
  • Added a new frame in the status bar for display of Tac32 messages.
  • Updated the Help files.


Version 1.1.4, Dec 31, 1997:
  • Corrected an error in calculating the Day of the Year.


Version 1.1.3, Dec 30, 1997: This version includes all of the outstanding suggestions and bug fixes that received from the beta testers.

New Features:

  • Sound Effects: Can now select All, Out-of-Lock Only or None.
  • GPS Receiver Parameters: The satellite activation table now highlights both satellites being tracked (green) and those which were previously tracked during the current session (cyan). This can be used to form a picture of the currently active satellite constellation over a period of 12 hours.
  • Help: Added context sensitive help control to all dialog boxes (the "?" at the top, right) and comments about using the F1 key to get dialog help. Using either of these methods will get direct access to a dialog's help screen. This will eventually be expanded to full context sensitive help in a future release.

Bug Fixes:

  • CTS: Use of CTS for the 1 PPS timing mark signal now works correctly.
  • T-RAIM: Additional comments have been added to the help file to explain some limitations and assumptions about the operation of T-RAIM and the "Kill 1 PPS on Fail" selection.
  • Logging: Corrected release documentation for Version 1.1.2 to include the new logging feature (see below).
  • Startup: Improved handling of the main clock type selection on program start to reset the clock and Registry to UTC if the Registry contains an illegal value.


Version 1.1.2, Dec 23, 1997: This version includes all of the outstanding suggestions and bug fixes that have been received from the beta testers.

Note 1: the Help files have been upgraded to match the latest changes and add new screens and new information topics.  Much of the detail about the latest changes can be found there. I need more feedback on the Help information.

Note 2: Many of the features in Tac32 are only available for those using full featured GPS receivers such as the Motorola 6-Pack and Oncore series.  Unavailable features are disabled where they appear in the various setup screens.

New Features:

  • Implemented logging capability (File menu).
  • The 1 PPS timing mark signal may now be connected to DCD, DSR or CTS
  • The main clock display may now be set to UTC, PC, LMST, or GMST.  It may also be set to PC-U to show the PC clock error (useful to watch for drift, etc.).
  • 1 PPS can be disabled on T-RAIM alarm (configurable on the Timing dialog).
  • Added Selective Availability SA and Anti-Spoofing (AS) tags to the other status conditions available on the satellite signal strength bars.
  • Active satellites are now highlighted on the satellite activation matrix in the Rx Mode dialog. This matrix also now includes Enable All and Disable All buttons.
  • The signal strength bars now go all the way down to zero.
  • The dialog size and state are now saved between sessions.  The dialog is limited to a maximum size equal to its optimal size.  You can use this capability to shrink the main screen down to show only the clock and use the maximize button to quickly view the entire screen.
  • All setup screens have Default buttons to get you back to a standard configuration quickly. The Rx setup screen includes both Nav and Timing default buttons.

Bug Fixes:

  • Corrected errors in display and internal management of T-RAIM parameters. Improved T-RAIM diagnostic and log messages.
  • Cancel now works correctly in Coax Calculator and Timing dialogs.
  • Improved error handling in Coax Calculator dialog.
  • Corrected the definitions of the totals boxes in the timing dialog (see the help for details).
  • Corrected an error in setting the Cable and Rx delay values in the Timing dialog screen.
  • Changed "Ionospheric Delay" On/Off to "Iono Corrections" Enable/Disable in the Rx Mode dialog to more accurately reflect the function of this control.


Version 1.1.1, Dec 15, 1997:
  • This version includes an important and long overdue correction! When operated in NMEA mode, including all Garmin receivers, some users have never been able to get Tac32 to work correctly. It turns out that the $GPRMC and $GPGGA messages were being rejected for certain locations because of a faulty validity test. This is now corrected.


Version 1.1.0, Dec 12, 1997:

This is the first BETA release. Tac32 now includes all the features included n the original design plan. It is a major upgrade! The following is a terse list of what has changed. There is a lot to play with in this release. Use the new Help files. There's lots of new information there.

New Features:

  • Initialization of the GPS receiver includes reference location (both Motorola and Garmin).
  • New Averaging Parameters dialog box
  • Help files are now up to date.
  • Clock synchronization can be set to 1/sec, 1/min, 1/hr or 1/day.
  • Can now set Reference position Manually or as a copy of either the average or current position data. Manual setup includes a built-in WGS-84 geoid model to aid in setting the altitude.
  • New Timing Setup dialog box to allow user adjustments to the 1pps timing mark signal. Includes a coax cable delay calculator with a large database of coax types.
  • Serial ports are now auto-detected so the list of available ports in the Serial Port Setup dialog box will accurately reflect the local computer's capability.
  • New GPS Receiver Mode Selections dialog box.  Permits the user full control over the GPS receiver's performance characteristics. Available selections vary based on receiver type.
  • Implemented audible and visual out-of-lock indicators. Also added out of lock information to the new Averaging dialog box (above).

Bug Fixes:

  • Averaging filter performance during the first few cycles was faulty.
  • Corrected an error calculating PC clock latency at the top of every minute.
  • Very small negative Latitudes and Longitudes (between 0 and -1 degree) now operate correctly for both input and display.
  • Initialization reliability improved.
  • Resizing the Rx Id view box now works correctly.
  • F1 key (Help) now works correctly.  This is a handy way to get quick access to help for a dialog box while it is open.


Version 1.0.16, Nov 2, 1997:

New Features:

  • GPS Week to the GPS Time window. Improved the raw data display for Motorola binary messages to show messages received but not decoded. Provide a full set of DOP information in Motorola binary mode. Display Average and Reference position data in the Navigation window. Set the reference location from the Current or the Average positions.

Bug Fixes:

  • Makes sure Motorola receivers are not left in idle mode. Corrected an error in the Set Serial Port/Search command which caused the result to always return "Mot NMEA". Corrected an error which sometimes prevented successful initialization, especially with Garmin receivers.
Version 1.0.15, Oct 26, 1997:
  • Fixed a bug which kept the PC time showing Daylight Savings time after time had switched to Standard time.
Version 1.0.14, Oct 24, 1997:
  • This version introduces a new display interface for the satellite data. Satellite and receiver status information is now displayed. Watch the SNR bars for satellite status messages! Also displayed is DOP information. The NMEA mode has more DOP and satellite-in-view information but the Mot Bin mode has lots of interesting satellite status information (shown on the SNR bars).