NexStar Resource Site

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Firmware Versions on the Original NexStar 5/8

Following is information previously posted by Aaron on his now defunct web site  I get asked so often about the different firmware versions that I felt it necessary to post this information on an active web site.  If anyone knows Aaron, please ask him to contact me for official permission to post this information.  Here it is exactly as posted before.  The only additional info I will mention is that there was a version update after - the newer version does not report a version number with the four-button power on trick and it now displays a warning if you attempt to slew to an object below the horizon.

Internal Firmware

For older NexStars, the firmware version was displayed on the hand controller when the NexStar was powered up for all the numbered versions below.   However, this doesn't happen with newer units, or with units that have an upgraded hand controller.  For these newer hand controllers, the four arrow buttons must be held down while turning on the NexStar in order to see the firmware version.

The version number, when displayed, consists of four numbers, separated by decimal points; i.e.  The four numbers are the version of the main EPROM, the ALT controller, the AZ microcontroller, and the hand controller, respectively.

There have been two versions of the main EPROM--2 and 3.  3 adds the moon as a GOTO object, but only with hand controller .7 or later.  Thus, people with won't have the moon as a GOTO object until upgrading the hand controller (i.e. to get the RS-232 upgrade).

There have also been two versions each of the ALT and AZ microcontrollers: .12 and .13.  It's not clear what .13 fixes, although it seems to address the runaway slewing problem.  Some early scopes have .12 ALT and .13 AZ microcontrollers (

There have been several versions of the hand controller.  Version .7 is needed (along with EPROM 3) for moon support; it may also address some European settings problems.  Version .9 fixes the RS232 lockup problem.  This version of the hand controller does not display version information on startup; however, the firmware version will be displayed if all four direction keys are held down when the scope is powered up.

Here are some versions that have been encountered: Initial release.   Actually, works very well! Addresses (but doesn't solve in all cases) "runaway slewing" problem. Moon is not a GOTO object, despite the version 3 main EPROM, because of the hand controller version.  (This seems to be an exceptional case: a newer base shipped with an older hand controller.) Adds moon as GOTO object.  Resolves problems with European settings.
2.x.x.9 Someone with an older version of the firmware who upgrades hand controllers to fix the RS232 bug will not have the moon as a goto object, and may have the runaway slew problem. Addresses RS232 bug, as above, but has moon as GOTO object.  Version number not displayed upon power-up. The latest known version.  As above, version number not displayed upon power-up.  It seems hand controller .10 is an attempt to address lingering RS-232 issues.

The firmware resides in two socketed EPROMS and three microcontrollers (two in the base, one in the hand controller).   Apparently, these can be mixed and matched to a certain extent (see chart above).   There is no way to update the firmware via software, and Celestron requires returning the base and/or the hand controller to update the firmware.

Celestron doesn't seem to have settled on an upgrade policy for owners with older versions yet.  I would imagine that the firmware would be upgraded under warranty if it contains a bona-fide bug.   Also, it seems that when scopes are replaced under warranty, they are supplied with the latest firmware.

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Michael Swanson
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