Old 486 Board for ECU??

[Mike from West Australia]

At 03:34 PM 30/4/2000 -0800, you wrote:
>"Peter D. Hipson" wrote:
>> 
>> Par ports are fast--much faster than the typical ECU of today. Memory...
>> Let's see, Windows 2000, 128 MB Ram, and a 10 Gig drive. Of course a flat
>> screen LCD display, and a minature keyboard would make a reasonable setup.
>
>The I/O speed isn't the problem.  The issue is: can you generate an
>output signal with one microsecond accuracy relative to an input signal?
> How about two outputs that might change at once?  Three?

Pardon !?

You don't need to generate an output within 1usec of getting an input.

As long as the output is generated with synchronism and within the
time it takes for a revolution/4 or 6 then you will be fine.

The CPU's I've seen in ECU's in last 20 years are *slow* 8 bit micros
that clock at around 4 to 12MHz. In fact in 1982 I did a Z80 based
EFI using a 4MHz CPU (tried 6 but too new). 

The Z80 NMI came from the ignition contact points (through fitlering)
which fired an injector. In the background the CPU would constantly
acquire AFM and engine temp readings and generate a number ready for
the next interrupt...

A 486 which clocks at 66MHz and has the OS/EFI routines in cache will
*easily* handle synchronous response to external real time events.
Heck it might be enough to look at the jitter on the crank angle
sensor. The problem would be MSDOS, not patched appropriately.

The timers on a 486 board are very well documented and the interrupt
structure is wide enough to set up a simple priority scheme...

The requirements for EFI is *well within* the hardware capacities
(timers, CPU speed, RAM) of a 486 - even at 20MHz and no cache.

Of course you need an ADC but only one of the inputs could be
considered as time critical and even that (AFM) can be asynchronous
with respect to engine cycles... ie Fast sampling helps but
AFM synchronous measurement is not required...

my 2c worth.



Rgds


Mike Massen

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