Rbob? 7747 vs. 8746 code & hardware
 

I did some poking around in a definition file for the $42 mask and what caught my eye was the "Options @ 0x0005" byte. Looking at the notes next to bit 6 I read the following: "MAT degrees for F132 table; Off=Inlet temp". This leads me to two questions... 1) What is the F132 table? And 2) Would I be naive to think that I could simply set this bit to 1 and install a MAT sensor (and, of course, change the lookup table to appropriate values for MAT temps instead of CTS temps)?

Option two sounds way too easy to be true so I did some more comparing. Looking at the pin-outs for the 7747 and 8746, I see that they are basically identical. The only exceptions are:

• Canister purge solenoid control @ A3
• VATS @ B6
• A.I.R. Converter solenoid @ C1
• MAT sensor @ C12
• A second "Injector 2" @ C15
• A second "Injector 1" @ D15

Does anyone know if the hardware portion of the ECM is the same and they just run different code?

Can you run a 8746 .bin in a 7747?

Is the difference in the code between these two ECMs located in the PROM, in the ROM or in both?

Thanks for any insight......

Either someone is entirely confused with that definition file or there is another $42 mask out there. The '747 has no code to read an IAT/MAT sensor. Can hook one up but it can't be used unless code is written for it.

The hardware for the '8746 & '7747 & '8063 is all identical. The only difference is the firmware in the two chips for the on-board ROM. Can't swap EPROMs among them.

RBob.

I was pretty sure the 7747 couldn't use the IAT/MAT or someone would have already done it. A lot of the code is the same between the 7747 and the 8746 so all I can assume is that the 'base' mask template is used for both ECMs and then developed differently for each application. It could be that with ECMs that do use that IAT/MAT, that you could toggle bit 6 @ 0x0005 and use MAT or CTS. The 7747s code probably never even checks that bit and therefore it could be either off or on and it wouldn't affect the outcome. Of course all of this is just a WAG base solely on conjecture and wild supposition.

I figured that the firmware between the 7747 and 8746 would be different disallowing the use of one .bin in the other, but thought it was worth asking.

Is there enough room available on the 7747's eprom to add the code to use the MAT? Of course that would be re-inventing the wheel and it would be easier to just use the 8746.... just curious how much available space is on the 7747 eprom to play with.

I need to answer you question in reverse order to make sence.
There is no room on the eprom for any code unless you delete code. All 4k is used for something relatively important, only the HUD stuff is completely worthless to us.
The ecm's are exactly the same except for the code on the rom and obviously the eproms are different for that reason. The rom has no code for the MAT in the 7747 so your options would be to run romless and then do whatever the hell you want, OR, remove code in the eprom, patch it so the ecm doesn't get confused, then insert ALL the mat code. Obviously since all 4k of the eprom is full of code, removing it and compressing the data would loose you either full fledged features OR resolution, depends on how good you are at the machine code for the 68hc11 :) . I know RBob is one of the best.