I've always been an indifferent programmer, and I have 0
experience with 68 asm. I could probably muddle through it and end
up with something that works though. Are you looking for someone
to make modifications to the MS source?
I've been thinking, and it may make more sense to use something
like the TPS input. MS has a neat built in tuning feature if you
hook up a wideband. It would be a shame to give up that
capability. The TPS on the other hand probably isn't necessary for
AC use as it is mostly concerned with throttle response. I am
assuming that you have no other inputs that are unused in your setup.
Josh
Mostly for some one to collabrate. Two heads are better than one.
Most of the time the other guy has a better idea :) I have got to
come up with a routine that calculates the coil dwell time
compensation as a function of RPM. The idea is turn on the current
in the coil 2 or 3 ms before you need the spark to fire.
We can connect the O2 sensor as long as you are running no lead
auto gas. A switch somewhere can turn it off and on. 100LL
destroys O2 sensors.
We got 8 channels of A to D and we are using only six.
Paul Lamar
I've run wideband sensors on cars with leaded race gas for
considerable time with little ill effects. To be sure, eventually
the lead will coat the sensor, but if you're only using it for
tuning, you can remove it once you're finished and plug the bung.
Isn't there some built in dwell time compensation in the ms
software? I was using the ms+spark-extra version. Have you checked
that one out? It was several years ago, they may have integrated it
with the baseline ms by now.
http://www.msextra.com/doc/index.html#ms1
http://www.msextra.com/doc/ms1extra/MS_Extra_Basic_Configuration_Manual.htm#rotary
Josh
Thats what I had in mind. By rearranging the chips I am going to
wind up with a lot of real estate left over. The cost will be lower
as well. Use of the CD4050 buffer instead of transistors helps a
lot as well.
Yes on the dwell but I haven't found the source code yet. I
suspect that was done in C version. I have to support this so I am
sticking with asm.
Paul Lamar
Paul,
Open this file and search for "dwell". They've noted it fairly
well. I can't make heads or tails of the actual programming without studying
asm.
Josh
I did and this is what I came up with.
ldhx #0
sthx dwelldelay1
sthx dwelldelay2
sthx dwelldelay3
sthx dwelldelay4
sthx dwelldelay5
sthx dwelldelay6
Aha they used a look up table.
clr lowresH ; low res (0.1ms) timer
clr lowresL ;
lda dwellcrank_f
sta dwelldms ; initial dwell period
mov #$10,dwellush ; } high speed dwell delay,
; default of 4.1ms
clr dwellusl ; } until calc in main loop
bset SparkLSpeed,SparkBits ; At boot turn on low speed
ignition clr RevLimBits
From the looks of it they struggled with the problem a bit :)
They are using a timer that increments or decrements every .1ms.
Probably what happens is they preset the counter in the timer as a
function of RPM. Low count low RPM. High count high RPM I think Then
the timer interrupts the back ground program to fire the plugs when
it times out. Presto bingo.
Thanks Josh. I think I got it.
Here is how the Timebase Module works in the MC68HC908 :
Quote the MC68HC908 data sheet.
Paul Lamar
----------------------------------------------------------
Timebase Module (TBM)
16.1 Introduction
This section describes the timebase module (TBM). The TBM will
generate periodic interrupts at user selectable rates using a
counter clocked by the external crystal clock. This TBM version uses
15 divider stages, eight of which are user selectable.
16.2 Features
Features of the TBM module include:
[UTF-8?]⢠Software programmable 1-Hz, 4-Hz, 16-Hz, 256-Hz, 512-Hz, 1024-
Hz, 2048-Hz, and 4096-Hz periodic interrupt using external 32.768-
kHz crystal (We have)
[UTF-8?]⢠Configurable for operation during stop mode to allow periodic
wakeup from stop
16.3 Functional Description
NOTE
This module is designed for a 32.768-kHz oscillator. (that is what
we are using)
This module can generate a periodic interrupt by dividing the
crystal frequency, CGMXCLK. The counter is initialized to all 0s
when TBON bit is cleared. The counter, shown in Figure 16-1, starts
counting when the TBON bit is set. When the counter overflows at the
tap selected by TBR2:TBR0, the TBIF bit gets set.
If the TBIE bit is set, an interrupt request is sent to the CPU.
The TBIF flag is cleared by writing a 1 to the TACK bit. The first
time the TBIF flag is set after enabling the timebase module, the
interrupt is generated at approximately half of the overflow period.
Subsequent events occur at the exact period.
-------------------------------------------------------------------------
End of quote.
Piece of cake :) If I get this working that will allow using cheap
LS1 or RX8 coils. MSD CD's are expensive. Thanks for your help Josh.
Paul Lamar
Josh,
I think they use a dwell time delay timer to start the actual dwell
angle. So higher rpm actually uses less delay, and lower rpm should
be more delay.
Years ago I got totally confused when I first found "timing" used in
relation to "angle".
Since engine is mechanical, but ignition is electronic, they actually
live on two different "time" domain. Mechanical devices base all
timing on distance traveled. Therefore, its timing is based on angle
traveled, rather than time as in seconds or fractions thereof.
Since ignition coil needs time "K ms" to build up its energy content,
when translated to mechanical timing in degrees, we have to change
the amount of degrees in order to get a consistent K. Thus the
advance in Dwell angle at higher rpm to keep "K" a constant time to
charge up the coil.
The timer routing uses absolute time. Each revolution has a variable
amount of time depending on RPM. As RPM goes up, time becomes less.
To get the proper Dwell Angle, or a fixed time of K, we have to calculate
the time needed for a revolution at a given RPM, then subtract the
necessary Dwell Angle Time "K" to get the Dwell delay timer. I think
you are pointing to the Dwell delay timer thus the reason why it is
should be smaller at higher rpm.
Hope this makes sense and may be useful when someone tries to tune
their engine. As I think this is also true for fuel injection timer.
Henry Nee
Hi Henry,
How's it going. I am thinking of coming over there for awhile. How
much would an apartment cost me in Shenzhen by the month?
Here is a simple QB program that calculates the numbers.
CLS
PRINT "RPM RPS Ms Per Rev Deg per Ms "
FOR RPM = 2000 TO 8500 STEP 500
RPS = RPM / 60
MsPerRev = 1000 / RPS
PRINT USING "####"; RPM;
PRINT USING "######.###"; RPS;
PRINT USING "#######.###"; MsPerRev;
DegPerMs = 360 / MsPerRev
PRINT USING "#########.#"; DegPerMs
NEXT
Also check out the attached table file. The trouble with the Mac is
they don't automatically display attached files so you missed this
table in my last message :)
Paul Lamar
Could you use one pair(2 rotor) of Hall sensors at 97* BTC to turn the coil
charge current on and another pair to shut off or fire the coil BTC. My
thinking is this; 22* BTC for the timing and 45* for the charge time at
7500RPM as per your chart. The dwell at low RPM is high but should not be a
problem as the amount of run time at low RPM in AC use is minimal.
Dale Davies
Right now there is only one external interrupt in the MC68HC908.
That would work but we would get too much dwell at lower RPM with just two and the
RX8 coils are susceptible to burn out. The dwell should be in the range of 10 to 2
ms. I could use my SuperKim interrupt encoder and have 8 external interrupts so there
could be 8 hall effect sensors on different radii. Then one would select which int to
turn on depending on the RPM.
I might just put that on the board anyway as that would greatly expand the power of
the MC68HC908.
BTW I heard from a guy in Oz recently that used the SuperKim to control a robot way
back when. reubenh@cyberneticzoo.com
http://cyberneticzoo.com/?p=5372
Paul Lamar
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