Hi James

Are the two cylinders connected to the same crankshaft? . If so,I'm surprised that Yamaha would need to use two mcu's! ...

Anyway , it is possible to use a 51 based mcu to control an entire engine (both fuel and ignition) as Bosch did for many years with their Motronic (Infieon based ) products.

for ignition I think that this may be what you seek..
http://perso.wanadoo.fr/transmic/gb89c2051.htm

these links may help you with the approach to the maths if you decide to add fuel injection.
http://www.megasquirt.info/index.html
http://www.diy-efi.org/efi332/eq...gorith.htm

The following (although based on the c167 mcu) shows an approach to using a single mcu to operate a multi cylinder engine.
The code can easily be converted to run on an Infineon c515 or c505 as they share the CAPCOM6 PCA unit.

Here you can view the details
http://www.hitex.co.uk/c166/fuelnote.html
http://www.infineon.com/cgi/ecrm...._oid=-8137
and the code
http://www.hitex.co.uk/download/...s/fuel.zip