[Color Computer] Re: [Coco] Motorheads and the CoCo...
yahoo at dvdplayersonly.com
Wed Jun 15 19:52:46 EDT 2005
Taxing the coco is a major concern with an SEFI system. So in my plans, the coco does not actually do all the work. It only handles engine management, while a separate board will actually do all the actual work of firing injectors(PWM), adjusting the idle air bleed stepper and controlling spark advance.
The coco will monitor MAP, MAF, O2 sensor, coolant temp, air temp, RPM and all the other required information to make the commands to the controller.
My thinking is that if the coco fails, crashes or otherwise is rendered inoperable, the controller will still function and run the engine in the "Limp Home Mode".
The rough drawings and parts list for the controller is not simple in any way. It is totally constructed using standard old TTL chips mostly, some other chips that do stuff like the PWM for the injectors, up/down counters and a lot of 555 timers. It will have 64K of static RAM also for mapping the RPM range and TPOS and MAP.
The mapped static RAM is preprogrammed by the coco after initial power is applied to the controller.
Too much to tell about this in one email.
I believe that the coco is fully capable of handling the management end of this system, even if it was written in RS-Basic.. but I'll use OS-9 because I like it.
Since the coco will have to load up software to do this, the controller will work fine during initial startup of the engine. Once the coco is online with things, it will make any necessary adjustment to the controller while the vehicle is in operation.
The reason I decided to use the old reliable 74XX and 74xxx, some 54x stuff to is speed and reliability. TTL is equal to about five million instruction per second. More than is necessary to control an engine at 6000 RPM(one hundred revs/second). Since 4-cycle engine timing is based on the camshaft in SEFI, we now are dealing with only fifty turns/sec.
Okay, some of you have engines that are good to 7500 RPM. This is still only 62.5 turns/sec on the cam.
Surely this could be done easily with something like a 68hc11 or some of the other magnificent microcontroller chips, but I'm crazy about the old TTL stuff and using a coco to control them.
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