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Well, I have my Old PJ0 ECU from an 89 Honda Accord.

I wanted to read it's ROM and see how the fuel tables were aranged but I found something odd.

Thsi ECU doesn't have an OKI MCU in it. It's made by Matsushita and has Matsushita and Hitachi Components in it. It doesn't have an external ROM either. It does have a RAM IC tough.

It seems to have a Matsushita 40 pin MCU labelled MN1221CA

I didn't find any information about this chip on google.

Anyone knows what kind of MCU is it and if it's possible to read it's contents?

Thanks.

I will post pictures of it soon.

Here's a scan from the PJ0-A03 PCB

Notice that I desoldered the 40 pin IC and installed a cheap socket. I also scraped off the clearcoat on the chips so they're easier to read.

I noticed that they made 4 more holes to the left of the RAM chip. That would make a total of 28 pins, just like a 27C256. Odd..

I found some INFO about the RAM itself

Part Number = MB8416-20F
Description = General-Purpose Static RAM - Low Standby Pwr 55uW
Manufacturer = Fujitsu Microelectronics
Number of Words = 2k
Bits Per Word = 8
t(acc) Max. (S) = 200n
tW Min (S) = 200n
Output Config = 3-State
Nom. Supp (V) = 5.0
Package = SO
Pins = 24
Military = N
Technology = CMOS

And the chip HD6301YOP (See attached file).

However, I can't seem to find any sort of info on those MN122* chips.

Hey C-Man... Are there any traces on the back of the board that hook up to the four extra holes? If so, where do the go?

Yup, there are traces to those holes. I'll scan the back of the PC board and post it here.

I noticed that there is no ttl connector on this board. I wonder if the MCU can be interfaced just like the OKI 8X51 with a ttl converter. I'll have a romboard adapter made with a ttl connector on it. Basicaly an adaptation from Doc's rom board with traces to the ttl pins directly.

Well, yesterday I checked where the ttl lines go on the OKI MCU and they go to pin 10 and 11.

There's nothing that goes to pin 10 and 11 on the matsushita MCU. I may be able to wire those to my max232 adapter and dump the ROM.

I got my hands on a California Emissions PJ0 and this one has OKI chips in it with an external ROM. Thsi might be a better starting point. I got so many projects at the same time this is nonsense hehe. Oh well, at least it's still getting somewhere.

Yeah, me too... Lets see... Dishhwasher R&R, Prelude Interior, Dishwasher Install in the rental, Engine R&R in sister-in-law's 4G Accord, Finish foglights, etc... Ack... That's not even mentioning the other two project cars...

Well, I got the Cali PJ0 in today.
Here's what it looks like

PJ0_L022 picture

And the BIN I extracted
PJ0_L022 ROM


Now for the ROM itself. This rom is 64k (256 kilobits) but honestly it could have been a 32k. I didn't see any abvious fuel table in there yet. There are a few tables but they are too odd to me.

I will compare this ROM with the other early Honda programs and see what I can do.

Now, I desperately need a Matsushita ECU ROM and see if it's compatible with this one.

I'll need help on this one.


Of course, I added all this to the Wiki

Well, I did find something in this ROM

At offset 62C8

There is something that looks like a 2 COL table. Could it be the fuel?

Same thing at 645E

There is also something at 662E (11col) and a similar table at 66F9

I'm still looking!

I wanted to see if the PJ0 could control a crank sensor. IT's not there from the factory but the I/0 controller could just use it if the ROM is coded accordingly.

Well, I noticed that one of the 2 wires for the crank, cyl and TDC sensor are all wired together on the my PK2 and PH3 ecus and they are just not connected to anything on the PJ0 !! This is pin B12, C2 and C4.

The wire is there, it's present on the dizzy, it goes to the ecu but the ECU just doesn't use them. They are basicaly a ground. My question is, WHY?!? why would they take the time to put a wire if it's to ground it anyway.

This leaves me with only 1 wire to add for the crank sensor on a PJ0 tough. It sure has alot of stuff connected to it so I don't know if I'll ever be able to add it but who knows.

Anyone has a clue on this?