Copyright Gene Chimahusky 2002 All Rights Reserved
Ok, for all you harware/software types here is one.
Update 11/22/2002
The word from Meade on the issue of corrupt eeprom rendering at least the AS494 useless is that 'it has been 'fixed' in later revisions of the firmware.
It also looks like the config register of the hc11, at offset 0x3f, was corrupted during the power down.
The symptoms of all led's extinguishing after boot can be duplicated by zero'ing the NOCOP bit in the register, which enables the deadman/watchdog timer in the HC11 to fire if the watchdog is not tickled every ~1second (based upon the init of register 0x3c). It seems the register should have this COP disabled because there is no code to tickle the watchdog in the given timeframe.
Again, thanks to Dick Seymour for a register dump from a 'live' 494 that shows the COP disabled and querying Meade about corrupt eeprom killing a 494 and checking that they do not use COP.
Update 11/20/2002 - Schematic added at end of page
Corrected statment about 'COP' - Computer Operating Properly being disabled in control register XX3F, not 'illegal opcode' as originally stated.
Update 11/19/2002
The cause of all the trouble seems to be the lack of a Low Voltage Reset circuit in the AS494. What happened was I had the 494 hooked up to a fairly hefty AC adapter that was not plugged in, I powered up the 494 and out of the corner of my eye saw the keypad light up, then fade. The capacitor in the ac adapter is pretty hefty so it drained slowly (2-3 seconds). It would not come back after that whether on battery or the AC supply. Bummer to say the least.
The symptoms at this point were turn it on, it would show the version and autostar logo, then turn all led's off and there would be a faint flicker running across the display. No key would cause any change.
I started reading the Motorola manual on the 68hc11 and saw that it offered some special boot modes. In order to interface to the 494 it required disconnecting from the base, supplying power on pins 1 & 8 of the connector, tapping into the serial TxD and RxD that run to the connector and feeding them to rs232 driver receiver chips (1488/1489 old tech but work!).
To bring it up in the 'special boot' mode requires grounding pin's 2 & 3 (MODA/B) of the hc11 then hitting it with a reset on pin 17. This invokes some masked code in the hc11 and sets it up for serial comm's with the Motorola SW called pcbug11.
See http://e-www.motorola.com/brdata/PDFDB/docs/M68HC11E.pdf for the hc11 manual.
Everything went fine after I learned to setup the chip's control registers for enabling writes to the internal eeprom, enabling the internal eeprom to be visible, and mode switching from 'special boot' to 'special test'.
Once in 'special boot' mode you can then transition the chip to 'special test' mode which puts it into expanded mode and makes the Meade flash code visible.
Dick Seymour provided me with a rom dump from a later version of the AS 494 so I could take a look at the init sequence. I did not see much of anything different except different address for the same routines (diff versions!). Ok, so what is wrong?
Update 11-20-2002 - I disabled the COP exception - "Computer Operating Properly" (not the 'illegal opcode' as stated originally)
in the control registers and rebooted normal. The 494 got farther, did not turn the led's off, saw it say 'Initializing' then 'Warning' but then the display started to flicker again with no other response.
I then held reset low, grounded the MODA/B pins and removed reset to bring it up in special boot mode again. I looked around at the stack trace that was available and things did not look to bad.
Ok, what the heck. I took the first 0xd2 bytes from the eeprom section of the dump supplied by Dick. Programmed them into the eeprom and hit reset.
Up it came!
Moral of the story, corrupt eeprom data can render at least an AS 494 totally inoperative, and a brown out on power can cause this to happen!!!
See last picture for the healthy patient!
End of update 11/19/2002
The microcontroller in the Autostar is a Motorola 68HC11E1 and it offers some very powerful debug capabilites when coupled with PCBUG11.
What you see here is the 494 powered externally and the pins 20 RxD of the 68hc11 goes to conntector pin 6 and TxD pin 21 of the hc11 go to connector pin 4.
What is required is to level shift these to rs232 to feed to your PC, i used a 1488/1489 232 receiver/trasmitter chips from the junk box.
The 68HC11 offers a 'special bootstrap' mode by holding Pins 2&3 (MODA/MODB) of the HC11 low and resetting via a low on pin 17 of the hc11.
The rest is magic courtesy the pcbug11 software from motorola.
It d/l's a small talker program to the hc11's ram and then opens lines of communications to the chip. What you see in the screen dump is the display of memory from 100 to 200 of the Autostar 494.
Updated 8/15/2004 - pins 20, 21 were swapped on diagram above
Thanks to Karsten from Germany in March 2004 for pointing the goof out to me.
Note: The text description above has been correct, the diagram was hosed.
