EFI: Memory Offset

Memory offset for Honda OBD1 ECU

  • 29c256
  • 27sf256
  • 29c512
  • 27sf512

These are almost the same IC. The specs are pretty close.

ATMEL 29c256 and ATMEL29c512 is the standard. Really great EEproms that are robust. No erase needed.

SST 27sf256 and 27sf512 are a bit different. The main thing, erase is needed for each write. I will post the technical papers in my next post. (Yes, I do not like these EEPROM very much, but not much I can do since Atmel discontinued their line)

I’ll be discussion the P28 but this fits the bill for most Honda ECU OBD/0/1/2 – reads on a high bit to be enabled.

On a 29c512 and a 27sf512 to enable reading you have to start writing at hex 08000 to 0ffff. You can store a dual image. If you want to do that just read the tech manual and it states what bit to change (not worth the hassle unless you built a fancy dual changer).

On hondata they have a mini FAQ on this change for the pocket programmer. I’ll post my procedure and then post their procedure:

Pocket Programer II
I shouldn’t have to post this but make sure your not using any devices that talk to the computer – Corrupt image files are easy to come by.

27SF512
(1) Erase
(2) Start buffer 08000
(3) Load Buffer (your bin file)
(4) Program Device
(5) Verify
(a) if failed – start (1)

Atmel Chip you can start at 2. Although, it is always recommended that you verify that it is blank.

o Yes, normal for the SST IC to not verify from time to time. Corruption happens – I should read the datasheet more and find out why; one day. You must repeat the steps. (That’s why I have no love for this IC)

Hondata recommends that you set the the start buffer back to 0 after. I don’t see why the need since 00000-08000 is erased anyway. Both methods work.

Taken from Hondata

The 27SF512 is a replacement for the 29C256.  There are some differences when programming the 27SF512 using the pocket programmer:

1. Ensure that you have the latest software version from http://xtronics.com/memory/updates.html


August 27, 2007, 04:00:59 PM

Here’s a break down of what you will need to be changed:

File Size           Chip            Buffer Start -> End         Chip Start -> End

4k (4096)       AT29C256      000000 -> 000FFF            007000 -> 007FFF
16k (16384)    AT29C256      000000 -> 003FFF            004000 -> 007FFF
32k (32768)    AT29C256      000000 -> 007FFF            000000 -> 007FFF
4k (4096)        27SF512        000000 -> 000FFF            00F000 -> 00FFFF
16k (16384)    27SF512        000000 -> 003FFF            00C000 -> 00FFFF
32k (32768)    27SF512        000000 -> 007FFF            008000 -> 00FFFF
56k (57344)    27SF512        000000 -> 00DFFF            002000 -> 00FFFF
64k (65536)    27SF512        000000 -> 00FFFF            000000 -> 00FFFF

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