VLT type 1 with shadow rom

Hal · Post by **Hal** » Mon Sep 21, 2009 9:10 pm

Hi all,
With regard to the 1k shadow rom, is it essential to remove it, or is just moving the link to disable it sufficient?

Is this only applicable for when you use the nistune board, or should this always be done when the main rom is modified?

Does anyone know the exact purpose of the shadow rom?
TIA

Matt · Post by **Matt** » Tue Sep 22, 2009 1:28 am

long and (technically) interesting story... a long time ago memory chips were very expensive

original Z31 1984-1985 computers used a 8K masked ROM which were cheaper and programmed in mass production

for map specific programming, this was done in a more expensive 1K Programmable ROM chip

ECUs evolved in 1986 requiring more code space, using 16K masked ROM

The specific programming for auto/manual etc was still done on the second 1K Programmable ROM chip

The jumper was used to indicate the chip was fitted and to use it

You must remove the chip and change the jumper, otherwise it will get confused basically

I have an original prototype VLT commodore ECU which has 4 x 4KB ROM chips fitted to a full size daughterboard. The last chip was removed and probably used with an emulator for programming/tuning the maps

Things have changed a lot since then, and I imagine Nissan would never have thought we could plug a USB NVRAM board into these and change all the maps

Hal · Post by **Hal** » Tue Sep 22, 2009 2:55 am

Hi Matt,
So I undertand you to be saying that any modification to the 16k rom, whether using nistune or by fitting an aftermarket 16k chip, requires the link changed and the complete removal of the 1k rom to avoid data confusion?

Matt · Post by **Matt** » Tue Sep 22, 2009 10:12 am

yes, otherwise it uses the 1K ROM chip maps instead. I found this out the hard way when first using RB30 ECUs and wondering why the map changes were not having any effect (K constant etc)

Hal · Post by **Hal** » Tue Sep 22, 2009 1:03 pm

Ok, then the next q. is why did they have the 1k in only the vl turbo computer and not the n/a, especially given that the position exists on the n/a board?
This suggests that the extra space was still needed for the turbo computer, yet clearly the turbo computer will run without it??

Matt · Post by **Matt** » Tue Sep 22, 2009 2:09 pm

the VL NA chips always used just base ROM from what I could see (no revision updates either)

R31 RB30 always had 16K (yellow dot for autos) and from memory same 16K ROM chip as the VLT but they had a slightly altered fuel map and DTC fuel pump code code added. They also had extra fuel pump control circuitry fitted (pulse generator, capacitor and a few resistors)

RB30ET had 16K also (orange dot for autos) with 1K installed. The 16K chip is different programming the VL RB30E with some slight code changes. I suspect the 1K chip may have been a revision update. Looking at the Nissan part#s there were several revisions of the ROM in this ECU

Extracting the 1K ROM chip and comparing the end of the maps against the overridden 16K ROM chip is the best way to determine the changes

Hal · Post by **Hal** » Tue Sep 22, 2009 11:37 pm

Matt wrote:Extracting the 1K ROM chip and comparing the end of the maps against the overridden 16K ROM chip is the best way to determine the changes

This was going to be my next step.

Matt · Post by **Matt** » Wed Sep 23, 2009 2:11 am

save you some trouble. except i havent done the VLT ones

I'll do that one the next one i receive. i have a box of chips, but not sure which ones are which

Hal · Post by **Hal** » Wed Sep 23, 2009 4:04 am

Interesting, these must be ecu's from skylines, as I've not seen a vl n/a ecu with the 1k chip installed.

Did you make up an adapter to read this chip, or do you have a programmer that can configure this pinout?