How the 4A-GE ECU works

[firehawk]

np303 Wrote:Would it be possible to find virgin OE MCUs and program them with updated change data if your just trying to correct for a some simple bolt ons with no real need for in-depth on the fly tuning?

I've also picked up a couple spare US ae86 ECU's. I've pulled the original MCU off in an attempt to read it with me SuperPro chip reader/writer I just picked up off ebay. I'm slowly trying to learn all this stuff.
I've yet to be able to read the data from the chip. I know it's a bit generic of a question, but what do I need to read the chip?

The MCU used in the bigport 4A-GE ECU is a clone of the Motorola MC6801 which has a read-only program memory. The devices were manufactured pre-programmed at the factory, so no "blank" 6801s exist - they are actually known as 6803s and have the internal ROM disabled. The 6801 is able to execute code from an external EPROM but the pins which are used for address/data buses are already in use for I/O. The pins would need to be re-mapped to other pins in the modified program code and the piggyback board which connects to the original MCU's socket.

I don't think the chip reader is able to get anything off the MCU because it is not re- or even one time programmable and therefore has no facilities for reading, programming or verifying the internal ROM. Only way to dump the code would be to build a small board which runs the MCU in test mode (mode 0) and executes code from an external EPROM with a simple program that dumps the contents of the internal ROM via serial line. You'll also need to program a PLD to decode the address lines into the enable signal for the EPROM.

Here's a nice program that can be adapted for dumping the 4A-GE ECU program;

http://www.8052.com/forum/read.phtml?id=128146

I'm currently working on building a board for dumping the code off my ECU and disassembling it but since I have a lot of other work to do on my car, this is currently somewhat on hold.