Apologies in advance, Please bare with me.

I have an old MSA... ECU with I'm looking to tune. I can see it uses two chips HHH and LLL, when it comes to reading the chips do I read/rewrite one at a time?

I'm confused as I've seen singular and H/L ori.files for the same make/model/year?

Yes you read and write one chip at the time. The original chips can not be written. They one time programmable. You must buy new chips for writing the new bins.

Oh OK thanks.

How is that some dumps I've seen from the same ECU has only one bin.file, why not H&L?

Becouse someone made export as a complete file and not as H & L files

I see.

So then does that file get copied onto both H&L chips, or is it split before writing to chips?

The file is split before writing.