Last updated: 10 July 2008
Jump to Today's Update
The Autostar is the computer controller for the Meade ETX, LX-90, DS-, DSX-, LXD and 4504 telescope families. It comes in two basic models:
Meade's advertising claimed that the 497 had a full megabyte, and the 495 had only
a half-megabyte, but every 495 anyone has investigated has had the full one megabyte,
and Meade's Autostar Updater program is happy to load any 495 with 497 firmware.
The principal differences between the 494 and the 497 are that the 497 has a full numeric keypad, and that the 494 has onoly 1/2 megabyte of memory.
In 2001, Meade produced a sightly updated 497. It has a different display module (only 14 pins on the connector, instead of 24) and lacks one chip (the 74vc244) which the older display module required. The "new" 14-pin display module is the same one used in the 494, and in the Autostar II's handbox. (The Autostar II is used in the LX200GPS, LX200R, RCX400 and MaxMount. In all of those mounts, the "brains" are in the telescope base and the handbox is merely a "dumb" peripheral which is not actually required for telescope operation)
Photographs of the insides of the 494 and both 497 models are here, along with sketches of the components.
This information will focus on the 497 Autostar, with comments about other models' differences.
If you take off the covers of your Autostar, you'll find that it contains a
two-sided circuit board.
One side has all of the active components on it (the "chips").
The other, key-side, is harder to expose. It has only the soldered contact pads for the conductive dots on the keypad. Those solder pads can oxidize over time, and cleaning them can help restore poor keypad sensitivity.
The Autostar's computer "scans" the contact pads, looking for ones which have been "short circuited" by the conductive dots bridging the solder pad fingers.
Beside every pad, hence behind every key, is a Light Emitting Diode (LED) to illuminate it.
The other, chip-covered, side is where all the fun happens.
Here are rough pictures of the components you'd see with the backs off:
Each rectangle in the picture is an integrated circuit, or "chip".
The main components are:
The computer portion of the Autostar is the Motorola 68HC11.
That chip includes on-chip timers, parallel and serial ports and an
which the Autostar uses to monitor the battery voltage.
The 68hc11 is an "8-bit" chip. That means that its primary calculations are done with temporary storage of only +127 to -128. It also has three 16-bit temporary storage and computation "registers", each capable of holding integer (whole) numbers in the range of +32767 to -32768 (or 65536 if all possible states are assumed positive or "unsigned"). It can only directly access ("address" in computer-speak) 65536 bytes of memory at once. That's its "address space". So how does it handle a megabyte of firmware? By "mapping" the megabyte into 32Kbyte "pages". The 32KB static ram always occupies the lower 32,768 addresses the 68hc11 can reach, or "page zero". The upper 32,768 addresses can be "overlaid" (or "mapped") by any 32KB piece of the Flash Ram. Similar to flipping pages in a book: whichever page is on top at the moment contains the text you'll see.
When the Autostar starts up, that lower 32KB static ram is empty. The initial state of the Flash Ram map (part of a parallel port in the 68hc11) points to the page which has the Emergency Load instructions in it. The internal hardware of the 68hc11 starts by fetching data from the top two bytes of its address space. Those two bytes are the "Reset Address", the place in the memory where the 68hc11 will begin executing instructions. Each program "page" of the Flash Ram contains the same data in the topmost 42 locations. If you're not holding down the Scroll Up and Enter key as the 68hc11 starts working, those initialization instructions tell the 68hc11 to "map" the second 32KB of Flash Ram into the active page. That page contains 13,000 bytes of firmware which are used frequently enough (or which -always- need to be accessible, such as the page mapper itself) that they're moved into the lower 32KB ram for constant access.
There is one more specialized chunk of memory in the Autostar. It's in the 68hc11 itself: a 512 byte piece of EEPROM (electrically erasable programmable read-only memory). That's where semi-permanent things like your Site, the previous start-up's date, your Owner Info, Training results and the Telescope Setup data are stored. They also survive power-downs, but are easier to update on a byte-by-byte basis than the Flash Ram.
The Flash Ram can be rewritten by the Autostar itself. It's the same type of memory
that is used by digital cameras. In order to write to it, it first has to be
erased. The chips Meade uses are erased in 64 Kbyte chunks. Herein lies a major
difference between the 497 and the Starfinder/494 programming. The 494 does
not allow updating of the program firmware itself.
You can only update the User Object area.
In earlier firmwares (before v30Eb) the 497 reserved the upper two 32KByte pages as "spare" space. Expansion of the program to provide additional features, such as PEC, has grown into that space, and removed the following feature:
The 497 offers 63KBytes for "User Bodies" and Tours. The Starfinder only 32KBytes.
A "deleted" object is not truly erased, it's merely "skipped". If you use the keypad to add/edit/delete a lot of satellites, comets, asteroids or User Objects, then eventually the available user-space fills. At that point the previous 497 firmware would tell you "File Space Full... reorganizing".
What it's doing is copying the -active- objects in the 63Kbytes to those upper "spare" pages. Then it -erases- the entire usual storage area. Then it copies the 63Kbytes (now cleaned of the deleted objects) back to the usual space.
Newer 497 firmwares and the 494/Starfinder either get confused or tell you "File Space Full", since they no longer have that extra space. So they cannot self-clean their User Body/Tour area. It requires connecting to a PC to run the Meade ASU (Updater) to "garbage collect" the user-freed space. The 494 also requires use of the 506 cable/converter accessory to connect to the PC.
Images and text © R. Seymour 2001,2007
Meade 497 ETX Autostar
Meade Starfinder / 494 Autostar
Here are the older and newer 497 Autostars for comparison.
Note the difference in the display cable size/placement.
Here is the 497 Autostar's key-contact side (the other side of the above photos).
Plus a detail shot of the contacts and illuminating LEDs (the white squares labeled D23 to D26) for the four slew keys.
The rubber key sheet has conductive dots which bridge the "fingers" of the contact areas.
Each key has two underlying dots which are on each side of the key's LED.
Images and text © R. Seymour 2001, 2008
Subject: "Born on" dating Sent: Sunday, February 11, 2001 22:42:27 From: firstname.lastname@example.org (richard seymour) The guts of the Autostar give only two hints as to date of "manufacture": (a) the paper label on the Flash Ram identifies what/when it was loaded with at the factory (b) many chips have a date code printed on the chip. It doesn't nail the -Autostar-, but it does give you a "not before" date. The code is four-digit: Year and Week-in-year So you'll see 9935 as being the 35th week of 1999. It's the second (or last) line on some chip's id codes. --dick
Subject: LCD modules' part numbers and datasheets Sent: Tuesday, July 8, 2008 07:52:38 From: richard seymour (email@example.com) (This is for the http://www.weasner.com/etx/autostar/as_schematic.html page. ) In the LXD75 Yahoo group, "bobdotfla" dug up what *appears* to be the part number for the "old" 497's LCD display. It's an Optrex DMC-50747NF-AK from Optrex America Inc. 73-1177-ND digikey part # (but not in stock) LCD MODULE 16 X 2 CHIP ON GLASS FSTN - Film Super-Twisted Nematic Its datasheet is available from Optrex: www.optrex.co.jp/us/product/catalog/pdf_dmc/50747ake.pdf and there's an "application note" to correct the above document's power supply description: http://www.optrex.com/SiteImages/PartList/APPNOTE/Technical%20Note%20TN-DMC-50747-01%20Note%20Rev.%200.0%2020040606.pdf Digikey catalog info (only $6.66 each!) This "old" module is not interchangeable with the 494, since it has the 24 pin connector, not the newer 14 pin connector. Chasing some of the "related parts" listed on the Digikey page, it looks like Optrex's DMC-16207H or DMC-16230N have the requisite 14-pin connector. Note: i have not purchased any of the above, so they may not be *exact* replacements have fun --dick
Return to the top of this page.
Go back to the Autostar Information page.
Go back to the ETX Home Page.