Brando5641

iTrader: (-1)

Sweet jesus... Awesome skills. Good read.

Cehbra

iTrader: (1)

Anyone could've done it - I just poured all my will into it, took me weeks to get to the bottom. I'm sure there are geniuses who could have done it in a few minutes...

92GTA

iTrader: (11)

This is one the BEST technical how-to articles I have ever seen on here, easily in the top 25 of the past 17 years I've been here.

Thank you for taking the time to publish all of this documentation you worked hard to figure out. It should help many people for decades to come!

Alex

TallTim

iTrader: (2)

Great work thanks for sharing! Reinforces the idea that many things that are simple at face value have a lot of complexity going on behind the scenes!

Cehbra

iTrader: (1)

Thanks for the compliment, Alex!!!
Makes me feel poud!

Cehbra

iTrader: (1)

Thanks! I totally agree. Once something is finished and running in daily routine we forget about all the work that went into its design.

RunawayRadio

iTrader: (2)

Now this was a good read! A couple years ago, i spent way too much time back tracking component part numbers and schematics for my dash to try and figure if it was even possible outside of a dedicated tool from GM to program the odo chip. Mine had burned out a couple resistors and it scrambled the odo eeprom when i bought my car, so swapping in a good used unit from a higher mileage dash was the only fix. that said, now the readout is 100kkm higher than what my car actually is and it still bugs me that it's not correct (even if i noted the mileage on the dash change). I eventually gave up when i realized the data was encrypted and way beyond my technical understanding.

This was a tremendous undertaking and it's hard to express just how impressed i am that you not only figured this out, but had the will to power through it in the first place. Excellent, excellent work!

And further to your concerns about the longevity of these chips, they will all eventually burn out in these cars and I have to wonder to myself what the group will do when there will be nobody around to replace them....kind of like owning a model t, but some of the most important parts are electronically encrypted and they don't make the black magic encoding tools anymore. And speaking of which, this entire thread should be a sticky for the digital dash crowd. It's way too useful.

Cehbra

iTrader: (1)

Thank you!

Glad my write-up is of use. You should at least be able to fix your mileage problem now.

777Shock777

iTrader: (1)

I'm happy to see something about the digital dash! Very nice work hacking!

A question a bit off topic, a lot of people (myself included) seem to have issues with the digits fading on these things.
Did you have to repair that on yours?

Cehbra

iTrader: (1)

I noticed that problem when I repaired the DIC. There a little pressure was sufficient to get the display working again. Apart from the odometer I wasn't able to test the other displays as I haven't put them in my car yet. I'll keep you posted on that matter.

mikedin

Thought I'd post this in case anyone was considering picking up one of these chips. Cehbra sent me one that I received a couple of weeks ago and I just installed it in my car a few days ago. It works great and I'm really thrilled to have my dash back to normal.

When I started my car before swapping the chip, the odometer would flash all 9's for a little while and then go blank. None of the buttons on the odometer would do anything, which also meant I couldn't switch from miles to km (I'm in Canada). Cehbra did *great* work on this and it's an important thing for all of us digital dash owners to have this documented since all of the odometer chips will eventually fail over time.

mikedin

I did have a little trouble opening up the dash to get the chip swapped. The connector on the back of the DIC (driver information center - the module with the SYS CHK button on it) is not long enough to pull out very far and the tabs on it block the rest of the dash piece from coming off so you can access the odometer board below it. I had to remove the lid and push the connector out from the inside using a screwdriver. And when re-installing I had to use a small pair of vice-grips to grasp the connector tab and pull it back onto the DIC. I didn't take pictures when I was doing it but here are some pics of a spare unit I have to show what I mean (next post)...

mikedin

two screws that need to be removed from the top of the unit

mikedin

arrow on left shows the ribbon cable that has to be disconnected in order to remove the lid. arrow on top shows where the cable connector will be attached in the car (which is not showing in the pic since it's on the car). I used a screwdriver to push the cable connector off of the (male) chip board connector that is showing. It worked best to alternate gently pushing on left, then right, then repeat until the connector came off. To re-install, I used vice grips to grab the connector tab and pull it back onto the chip board connector port.

Also, make sure to re-install the new chip in the same direction as the old one (it will fit both ways). Installing in the wrong direction will get you flashing 9's. Hopefully this will help speed up the process for someone else doing this.

Cehbra

iTrader: (1)

Thank you for the feedback mikedin. This is valuable new information about the DIC!

And I'm glad the chip works. You're the first to try, thanks for your confidence!

mikedin

np, I love that you documented everything here. There seems to be a lot of mystery surrounding the digital dashes and your post is the best I've seen to open up some of this. The odometer doesn't do any fancy encryption, it just uses a few simple tricks and basic technology (by today's standards) that was readily available in the 80's. Hard to figure out for sure but pretty straight forward once it's documented. Great work!

scoflaw

iTrader: (2)

Just encountered a problem with my 88 gta digital odo. Was working perfectly, removed dash to replace a backlight bulb and upon installation , odo is completely blank. Dic works fine. All I have is a backlight. Any suggestions would be appreciated.

RunawayRadio

iTrader: (2)

Would be best to start a new thread for this one. It could be a number of things.

Cehbra

iTrader: (1)

RunawayRadio is probably right, a new thread would bring more answers.

A quick suggestion: the odometer board goes in as the last, maybe it's not pushed in far enough. Mine needed a hard push to make a good connection with the connector on the housing.

scoflaw

iTrader: (2)

Done about enough pushing pulling, connecting , disconnecting. Was just working fine. Dunno

Resolved..After removing just the DIC, I could see that the odo plug had pushed back and wasn't making a connection. Thanks

MDS85

I also got a new Chip from Cehbra. I have 3 digital dashes, none of them working properly. So i swapped all boards from the dashes until everything works fine. Only the DIC and the odometer failed to work (flashing 999999). after installing the new chip the odometer lit up like it should be and after testing it for about 100 km everything works fine.

I can recommend using the chip. Installing is easy if you know how to get to it. I also switched the old bulps do LED, so the dash is now better to read and there is no more heating problem (the plastic already at some burn marks from the old bulbs).

So next step, getting the DIC back to work

eseibel67

I had the 99999.9 issue and had to buy a complete digital cluster/DIC/odometer In order to get the odometer to work. At the time, this was the best alternative because it was the only way to have a functioning odometer. Even though the mileage shows is over 100,000 higher than actual, it's still nice to be able to play with the mileage features.




Would have been nice to know a replacement chip can now be had.


Incredible job of figuring it out by Cehbra, and even though I didn't know what you were talking about, I still enjoyed reading it. Thanks!

Cehbra

iTrader: (1)

Nice to see it working, thanks for posting up!
And keep the pics coming in, too!

Cehbra

iTrader: (1)

Thank you sir!
In case you want to have the correct mileage you can send me your chip and I'll reprogram it if you cover the costs for shipping.

Cehbra

iTrader: (1)

Time to resurrect this thread!

I was asked by a member on this forum if I could come back to the problem I talked about earlier - specifically on how to completely reset the odometer to read 0.0 miles (the least possible was 10.0 miles at the time). So I dug up my old setup and did some more testing.

As this thread serves as my documentation on that subject, here is the addendum on how to reset the odometer to 0.0 miles (it wasn't all that difficult really lol):

Cehbra

iTrader: (1)

Here again is the instruction on how to scramble the encoded mileage (post #40):



Now as we need 0 miles we can fill in all the colored nibbles/cells from the "reading" row with 0000, thus only nibble 4 and 5 remain void.

Nibbles 4 and 5 is the data integrity information and is calculated as follows (see post #44):

• Cross add all the mileage nibbles (pos 0, 1, 2, 3, 6, 7 and X) to form the first checksum (cs1)
• divide that first checksum by 5
• here’s the translation table to calculate the second checksum (cs2) from the first:

Well the cross total is 0, divided by 5 is still 0, making cs1 0 and thus cs2 10. As stated in post #45 the sum of nibble 4 and 5 must give cs2, so in our case nibble 4 could be 8 and nibble 5 could be 2.

Thus a valid storage location would be 00008200 for example. Now breaking the rule of a 10 mile difference between two storage locations we would concatenate two (or all 8) zero mile values to form a pattern like this:

0000820000008200000082000000820000008200000082000000820000008200

or

0000820000008200000000000000000000000000000000000000000000000000

Cehbra

iTrader: (1)

Of course - as stated in post #45 - the two summands that give cs2 can be random integers < cs2, thus 7+3 should work in that case as well:

0000820000007300000000000000000000000000000000000000000000000000

I confirmed this digit sequence to work equally.

Cehbra

iTrader: (1)

As it looks there are not many more secrets left, the biggest one being the threshold on when that last digit before the comma changes from 0 to 5. I might tackle that some time. For now I hope that new information is of use to someone.

Cheers!

Bob88GTA

iTrader: (2)

Cehbra.....I AM IN AWE. I read through this whole post and while I find this all interesting, There is no WAY I could do what you have done ! Bravo, Kudo's to you!! What is your profession??
On another note..
I also have the Digital Dash on my 88 GTA. I owned this car from day one. It currently has 194k miles on it. Every thing works on mine except depending on the digital number on the odometer display, sometimes the number isn't complete, as in say the number "4" in pic is supposed to be a "9" may not have all it's outline...sorta like this:



Can this be repaired with a new chip with my actual mileage put on it?

Thanks!!

Cehbra

iTrader: (1)

Thanks!
I'm just a physician, that's why it took me weeks and weeks to crack that algorithm. An engineer could have done that in minutes. And I'm sure a mathematician would laugh at my scanty abilities. But anyways it got the job done

Actually I'm getting a similar problem with my driver information center. I believe it has to do with the contacts in the LCD. I think it could be repaired though - I'll dig into it and keep you up to date on my findings.

A new chip will most likely not change anything about your problem. Even if there are just small errors with the stored numbers in the chip the odometer will immediately display flashing 9's. As yours is displaying a meaningful number I assume your EEPROM is fine.

Cehbra

iTrader: (1)

By the way, your dash looks extremely clean!

Bob88GTA

iTrader: (2)

A physician, good for you! I'm an engineer and wouldn't attempt it!

Thanks for the response. I may just pull the LCD out of the pin sockets and gently clean each pin and re-install and see what happens. I barely drive it enough anymore to be a big concern. It just hangs out looking nice.
Thanks again!! Keep up the great work!

Bob88GTA

iTrader: (2)

Actually THIS one is mine.... Yeah its pretty clean.

Cehbra

iTrader: (1)

You're too modest, Bob!

Cehbra

iTrader: (1)

Here's the very last part: as I stated there is a difference between the mileage we encode with the formula above (post #40) and the result that's displayed on the odometer, the last digit being a "0" instead of a "5" for a very low mileage.

That switch occurs between 120 and 135. Meaning: values encoded with the above method starting from 135 miles will be displayed correctly, but values less than that will have a zero as the last digit. So departing from the "10 miles difference" rule there is a gap of 15 miles in this particular location.

Cehbra

iTrader: (1)

To round that thread off - and as a courtesy - I have decided to make my application available to people who are interested in that matter. It is attached to this post as a zip file, containing one .exe file with the name NCR52801Decode.exe.

It's a Windows 32 bit application, best run on 100 % font size.

Cehbra

iTrader: (1)

You are free to use the software, provided it's not used commercially and not abused to counterfeit odometer readings.

Cehbra

iTrader: (1)

In the first tab (Encode) the desired odometer reading is entered. Be sure to indicate whether you want to encode miles or kilometers. The app will give you a choice of two values if the mileage doesn't have a 5 as the last digit (depending on other factors, as well, see posts in this thread).

The odometer reading is always encoded in and rounded to miles as this is the internal storage unit of the digital dash odometer.

By pressing "Encode" the mileage is encoded into a hex string with 256 bit ("Code"), which can be copied to the clipboard or saved to a text file. From the text file you can program an NCR 52801 chip.

The four edit fields in the middle are just for insights on how the values are generated and are only for people interested in that particular matter.

Cehbra

iTrader: (1)

Now if you want to analyze a chip you can open its contents in the second tab (Analyze). Either you can open a text file with the load button or paste the hex string into the "code" field.

By pressing the Analyze button the string is decoded and the contents of each of the 8 storage locations is evaluated including its checksum. If you have a faulty chip displaying flashing 999999.9 you should see where the problem is. You will probably have to read through this thread to analyze the exact problem.

Cehbra

iTrader: (1)

That's it.

I think most of the questions should be answered concerning the internals of the GTA/Trans Am digital dash odometer EEPROM. If there are things I haven't considered or if you find errors in my algorithm or bugs in the app feel free to post things here.

RunawayRadio

iTrader: (2)

Now this is one of the best threads i've watched evolve here on the forum. Physician or not, you've done the community a great service with the care you've put into this!

TallTim

iTrader: (2)

WHAAAAT Cehbra is a physician and he's posting binary and a custom app to help TGO members? I've been in IT since the DOS days - man you you have another career waiting for you when you are ready!

PS Heh heh he said "nibble"

scooter

iTrader: (11)

firebirddude142

iTrader: (19)

Cehbra

iTrader: (1)

Thanks, I hope the information in this thread will be useful to you. There's more information on my digital dash swap here:
https://www.thirdgen.org/forums/inte...dash-swap.html

As for the different versions, the main difference is the tach display, which was S-shaped in 86 and C-shaped 87-88, plus some minor differences like a missing button in 86. Take a look here:
https://www.thirdgen.org/forums/memb...2-digital.html

Electrically there is no difference. I swapped an 88 version into my car, but the 86 unit I have works equally well. The algorithm to code the chip apparently is identical, too

BizJetTech

iTrader: (3)

Just ran across this topic - Lots of good info here - BUT I want to go the other way - I have a 100% factory original 1987 GTA with a perfectly working digital dash in mint condition.
I'm considering removing all the digital dash parts, including wiring, etc and replace with standard dash - I know it is a big job but thinking
it must be possible? Anyone ever done it ??

If I decide to do it I'd be hoping to find someone who is wanting to make a trade - standard dash parts and wiring for my digital dash parts and wiring.

still kicking it around.....any thoughts??

Cehbra

iTrader: (1)

Wow that digital dash definitely looks nice! How many miles do you have on it?

As for the digital to analog conversion, that can definitely be done. You will have several options, either leave the harness and just change the connectors, or switch to a matching analog harness. Anyways you won't have to bother with all the quirks I had to as the dash carrier, the bezels and buttons and most everything will not have to be changed.

scooter

iTrader: (11)

Anything is possible, but that looks like a low mile car. I wouldn't go messing with it

Swapping the harness is the only way the other person would really get full functionality out of the digital dash. Swapping harnesses and dash carriers would be easiest, IMO

BizJetTech

iTrader: (3)

44,000 miles on it

BizJetTech

iTrader: (3)

Yeah, I would swap out the entire harness and dash carriers......I may just sell it and pick up a Formula 350.....still thinking about it....
Just not a fan of the digital dash......here is the car - it's pretty minty....