Elec Dash Queston

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Elec Dash Queston

January 14, 2007, 11:16:04 AM

Can the milage be Zero'd out? On the car I'm working on now I would like to set the odometer back to Zero.

THanks. It is the XR7 digital dash

Elec Dash Queston

Reply #1 – January 14, 2007, 11:29:23 AM

Quote from: 5.8fastcat;123741

Can the milage be Zero'd out? On the car I'm working on now I would like to set the odometer back to Zero.

THanks. It is the XR7 digital dash

I'll try to check this for You this week, I need the same thing for Me, I have a lot of dig clusters here, I'll try to do this between two jobs:hick: .

But I'm not sure if it possible without major mod, I'll check that.

I'll let You know as soon as possible...

Have a nice day,

Elec Dash Queston

Reply #2 – January 14, 2007, 04:20:48 PM

we tried this a couple years ago,, look at the archive thread masterblaster did up. Bondo cougar could not get it to reset either clocking it to all 1's or zeros on the processor. I tried a couple other ways and could not change anything along the lines of the firmware loaded on the processor. Other than that , one other issue was the legal one.

It can be done,, we just dont know how yet.

Elec Dash Queston

Reply #3 – January 14, 2007, 11:32:34 PM

In Ky if the milage is over 100K they say it EXCEEDS MECHINAICAL LIMITS. My black car rest @ 199K miles. I don't know if that helps or not.

Thanks for the info.

I have some extra dashes if you need one to practice on.

Elec Dash Queston

Reply #4 – January 19, 2007, 09:34:36 PM

Bump

Elec Dash Queston

Reply #5 – January 20, 2007, 05:15:17 AM

i agree with the bump,, but if this gets figured out, i guess it will have to be deleted quickly:D

on a side note bout the digi displays, i have not forgotten about the HUD display. I have a spare still waiting for a fun day to "flip the lense".

did i say HUD display? that redundant:hick:

Elec Dash Queston

Reply #6 – January 20, 2007, 09:15:09 PM

IIRC, in the original BondoCougar thread on the old message board, he tried to reset the odometer but it didn't work.

Then again I'm old and forgetful now.

Elec Dash Queston

Reply #7 – January 21, 2007, 11:45:33 PM

After seeing 5.8fastcat's work on the car rotisery, I'm remotivated to look at this thing. Anything to help the Masters of these cars!

Besides, I have a better oscilloscope that might make things easier.

I don't think there is any jumper to set that will do this trick, I think the one memory chip in it has to be reprogrammed. The mileage is coded in a weird way, since nonvolatile memory was not too reliable in the 80's , so they rewrote the same numbers in several ways. The puzzle is to figure out how things are coded. I'll clear off the bench & take another look at it.

Resetting Digital Odometer to 0 SOLVED

Reply #8 – February 11, 2007, 05:14:37 PM

This modification to reset mileage to zero (or for that matter, setting it to almost anything else) has been figured out.

Its unfortunately not a simple jumper sort of fix, you actually have to remove the memory chip, put it into a solderless breadboard, and use some means to literally toggle the lines to read and rewrite the data into the chip.

There were two parts to this task, one which was completely solved, and a second part that is still not completely finished.

1) Getting the data sheet on the 1985 era nonvolatile memory chip made by Nitron/NCR, a company no longer supporting this device. These signals to/from the memory were probed in the past, but we couldn't make sense of what was data and what was address values. I found a datasheet from someone on a 1980's era computing forum when I posted for help. Someone actually had a 1985 databook on their shelf.

2) Figuring out how the odometer data is stored. The odometer data is stored as two 16 bit words (32 bits total). It is stored in MILES in 0.0625 mile resolution. Each 16 bit word has the 3 upper bits devoted to parity. I haven't really figured out how the 3 bit parity is calculated, but it was easy enough to take a guess for the 0 miles case.

While the nonvolatile memory has a bulk erase pin on it, that sets all internal memory values to 0. However, the parity values for all zero data is not zero, so resetting all memory locations to 0 results in a permanent "ERROR" display on the odometer. Likewise setting it to all 1's also results in "ERROR". I think thats why if you look carefully at the memory integrated circuit, everyone I have seen has a color stripe on it. I bet the color stripe indicated the chip was preprogrammed, not just straight from the memory vendor. Nonvolatile memory was sort of obscure in the 80's and also not reliable. In fact the odometer value is wrote to a rotating pair of 1 of 8 locations about every 10 miles to minimize the amount of writes. Theoretically if you killed battery power every 10 miles you could keep your current mileage.

Turns out (I guessed), that if the data bits are all zero to get 0 miles on the odometer, the parity bits must be all 1's.

Which means the way you get the odometer to reset to 0 involves:
1) Removing the memory chip from the board
2) Reprogramming the two 16 bit data locations to
1110000000000000 1110000000000000 ( Decimal 57344)
3) Reinstalling the memory chip

Likewise, any mileage value can be stored using the same method, but a guess on the way the upper 3 parity bits must be done.

I'll post the information in detail as soon as I write it up. Anyone who enjoys puzzles may be able to figure out how the 3 parity bits are calculated, as I have some spreadsheets where the bit sequences for several mileage values are shown. While its straightforward to see how the mileage equals a given bit sequence, the upper 3 parity bits are still a mystery to me.

Elec Dash Queston

Reply #9 – February 11, 2007, 07:58:07 PM

Here's the detailed info for the record.....

5.8fastcat I PM'ed you with my address to send your cluster.

This is information on the digital odometer in many base and full digital clusters. The odometer is constructed using Motorola liquid crystal display drivers, a 4 MHz Motorola MC6805 CPU, and an NCR nonvolatile memory chip. It counts pulses from the speedo gear located in the transmission, and stores the equivalent mileage into the memory about every 10 miles, or when the ignition switch is turned off.

Need to exchange mileage between two digital odometer clusters?

- You need to disassemble the cluster and desolder and swap IC3 from the speedo/odometer module

Need to change mileage numbers or reset to zero after an engine rebuild?

- Its not very easy unless you can toggle 6 TTL lines using either your PC or some other programmable device, IC3 must be removed and reprogrammed with the decimal values 57344 across the 16 memory locations.

Detailed background information on the inner workings of the digital odometer are given here, along with the binary patterns to reset to 0 miles, along with how the bits are stored:
http://mysite.verizon.net/junkyardjoe/DigitalOdometerFunction.pdf

The patents of the digital odometer which describes a lot of work that Ford had to do to ensure odometer integrity especially with the nonvolatile memory that was available in the 1980's.
http://mysite.verizon.net/junkyardjoe/4710888_Odometer_Patent.pdf

http://mysite.verizon.net/junkyardjoe/4803646_Odometer_Patent.pdf
The data sheet on the memory integrated circuit (not the same exact number, but seems to be completely equivalent, pin for pin, and all commands)
http://mysite.verizon.net/junkyardjoe/ncrmemory1.pdf
http://mysite.verizon.net/junkyardjoe/ncrmemory2.pdf

Want a puzzle to solve and yearn to be a binary speaking geek? Below is a spreadsheet of mileage values and the bits stored for each. An unknown is how to calculate the 3 bit parity (in the yellow columns) based on the bit data

http://mysite.verizon.net/junkyardjoe/odometervalues.xls

Elec Dash Queston

Reply #10 – February 11, 2007, 10:51:56 PM

i find it very curious that the leading 1's are in an octal (base

pattern.

did you notice that? i know everythng eventually comes back to binary to cypher but its still odd.

maybe youc could try different comboinations of the three parity bits, all 7 of them and see what happens.
000=this one is out
001
011
100
101
110
111= this one is out
ect,,,
i dont have a pulse gen or oscope,, wish i did.

did you ever find out if this is a eeprom? If it aint,, it probably cant be cleared either.,, one time use thing wouldnt you think?

Elec Dash Queston

Reply #11 – February 12, 2007, 12:44:59 AM

These guys figured it out.

http://www.speedometerwork.com/

Elec Dash Queston

Reply #12 – February 12, 2007, 11:13:30 PM

Quote

i find it very curious that the leading 1's are in an octal (base pattern.

Its only octal because the designer decided to allocate 3 bits for "parity", as stated in the patent. They have 32 bits to play with, and chose to use 6 total for parity.

Looking at Wikipedia, parity is usually associated with the number of 1's in the word. Since the 0000 mileage results in these three parity bits being all 1's (I found by trial and error, just as you suggested!), I bet the 13 bits that make up the data are broken up into three groups perhaps? And each group gets one of the three parity bits. And likely a parity bit is 1 when there is an even (including 0, eg 0,2,4,...) number of 1's.

Quote

did you ever find out if this is a eeprom? If it aint,, it probably cant be cleared either.,, one time use thing wouldnt you think?

The data sheet for the part is in the links I put up. It is an EEPROM, and does have an erase pin. Hold the pin high and all locations get reset to 0000 0000 0000 0000. But this results in incorrect parity (there must be 3 1's in bit locations 15/14/13) so the odometer reads "Error".

Could spend more time figuring out the parity, but we now know the bits to set to reset the odometer! The patents are an interesting read that shows all the things the designers were worried about. I wonder if there is other more engine related information on the Fox cars in the patent data base?

Quote

These guys figured it out.

Now where is the fun and challenge in that? :bricks1: Its cheaper doing it yourself I bet.

Elec Dash Queston

Reply #13 – February 13, 2007, 12:28:15 AM

sorry, im guilty of not opening the link you put up. I wonder what the odds are of something similar,, noting the input from the speedo. It might take years for it to make it to zero. Sound possible? or sound stupid?

I tried to open up the pdf's,, dial up and 15 min later no go. is the pn of the NCR on the other orig link?.

Another thing ill bring up which might be useless but may help. What about that one digit that never changes,,, when you hit 200k miles,, the 1 does not change to a two. Could that have an effect on something?

Elec Dash Queston

Reply #14 – February 13, 2007, 02:08:12 PM

Thanks Bondo,