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Hi Matt,

Just giving some comments for now. No progress made yet since the last post.

NSX ECU's MCU mode select circuit is also in the upper left corner (see the area around R424 in the diagram I posted). So I do intend to install some jumpers to mode change on demand.

I still can't be 100% sure how your additional 2-4 decoder is working (or not working). If you have the schematics ready, let me know and hopefully I can give you my 2 cents.

About the RAM, that address range (F800-F8FF) is actually not part of the internal RAM (FB80-FF7F). So my next guess would be, is there yet another external device on the bus that the MCU is talking to. It may be an output only device if it's never read from. If this is setup the same way on the NSX ECU, I will find it once I map out all the digital logic.

Will update again in a few days once I spend more time on this.

Thanks.

Eddy

<blockquote data-quote="Eddy" data-source="post: 1489901" data-attributes="member: 5906">Hi Matt,Just giving some comments for now.&nbsp; No progress made yet since the last post.NSX ECU&#039;s MCU mode select circuit is also in the upper left corner (see the area around R424 in the diagram I posted).&nbsp; So I do intend to install some jumpers to mode change on demand.I still can&#039;t be 100% sure how your additional 2-4 decoder is working (or not working).&nbsp; If you have the schematics ready, let me know and hopefully I can give you my 2 cents.About the RAM, that address range (F800-F8FF) is actually not part of the internal RAM (FB80-FF7F).&nbsp; So my next guess would be, is there yet another external device on the bus that the MCU is talking to.&nbsp; It may be an output only device if it&#039;s never read from.&nbsp; If this is setup the same way on the NSX ECU, I will find it once I map out all the digital logic.Will update again in a few days once I spend more time on this.Thanks.Eddy</blockquote>

[QUOTE="Eddy, post: 1489901, member: 5906"] Hi Matt, Just giving some comments for now. No progress made yet since the last post. NSX ECU's MCU mode select circuit is also in the upper left corner (see the area around R424 in the diagram I posted). So I do intend to install some jumpers to mode change on demand. I still can't be 100% sure how your additional 2-4 decoder is working (or not working). If you have the schematics ready, let me know and hopefully I can give you my 2 cents. About the RAM, that address range (F800-F8FF) is actually not part of the internal RAM (FB80-FF7F). So my next guess would be, is there yet another external device on the bus that the MCU is talking to. It may be an output only device if it's never read from. If this is setup the same way on the NSX ECU, I will find it once I map out all the digital logic. Will update again in a few days once I spend more time on this. Thanks. Eddy [/QUOTE]

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