Reference Pulses, Time Between Reference Pulses, etc.

[84Elky]

Would appreciate the brain trust weighing in on this. In going thorough the $8D code reviewing the start-up logic, have been trying to understand the difference between Distributor Reference Pulses (DRP) and Time Between DRPs (TBDRP). Have searched forums and posts and have read until my head hurts. The result is a lot of conflicting information.

So would like to start with this (‘7730, $8D, V8, TPI, External coil HEI):

• How many DRPs per crankshaft revolution?
• How are DRPs calculated?
• How is TBDRP calculated?
• TBDRP seems to be referred to as the “Reference Period”. Is that correct? What does that really mean?
• How do both DRP and TBDRP relate to Injector Base Pulse Width (BPW), if at all?

Part of my confusion comes from how a $8D ADX file converts some raw data. It uses the same Conversion Factor of 15.26 (assume this is uSec per DRP???) for reporting both TBDRP and Injector BPW.

Just some of many questions. Would really like to understand this so let’s start a discussion.

[1project2many]

DRP is a cycle of low to high to low voltage generated by the ignition module. There are four per revolution on the V8 engine. They are counted, not calculated.

Time between pulses is elapsed time between pulses. It is measured by reading a counter each time a reference pulse occurs.

"Reference period" is the time between distributor reference pulses. It really means the time between the falling edge of two consecutive pulses.

Time between pulses and number of cylinders can be used together to determine RPM. That variable is used frequently.

Injector pulses, in synchronous fire mode, occur in synchronization with DRP's.,

[84Elky]

DRP is a cycle of low to high to low voltage generated by the ignition module. There are four per revolution on the V8 engine. They are counted, not calculated.

Time between pulses is elapsed time between pulses. It is measured by reading a counter each time a reference pulse occurs.

"Reference period" is the time between distributor reference pulses. It really means the time between the falling edge of two consecutive pulses.

Time between pulses and number of cylinders can be used together to determine RPM. That variable is used frequently.

Injector pulses, in synchronous fire mode, occur in synchronization with DRP's.,

1Proj – Thanks for the prompt reply. With that and some math, think I’ve solved the nagging problem I was having with understanding the uses and meanings of Pulses, Periods, etc. Maybe others are having the same issue.

Here’s why the confusion. The $8D ANHT and AUJP code hacks both describe the pre-start, spin-up RPM threshold to be 300 RPM before the engine can be considered running. No problem there. And that RPM is associated with a variable (L801A) having a value of 0x0CCD = 3277d. Further, this value is compared against L00B3=CURRENT MNR LOOP DRP PERIOD to see if the engine is turning over enough to allow starting.

So in order to compare something apples-to-apples, if the comment on L00B3 is correct, that means L801A has to be 3277 DRP PERIODS as well. But it does not appear to be that. Rather, it seems that Distributor Reference Pulses and/or Reference Periods are used at times as a descriptor when ECM Pulses and/or ECM Reference Periods should be used. This is borne out by the fact that at 300 RPM, there would be only 1200d DRPs; yet the variable used for 300 RPM in the code is 3277d and not 1200d. What appears to happen is the ECM reads the Distributor Pulses, converts them to ECM Pulses with a base frequency of 65536Hz and then outputs the equivalent ECM Reference Periods into variable L00B3.

To further support this, the comparison in the code is such that the compared values cannot be Pulses of any kind, because the smaller the number, the larger the equivalent RPM. That relationship can only occur with Reference Periods/Time Between Pulses which have an inverse relationship with RPM (the smaller the value, the larger the RPM). Code snippet below:

ldx     *L00B3                  ; CURRENT MNR LOOP DRP PERIOD
cpx     L801A                   ; 300 RPM [= $0CCD, 3277d], START UP RPM [See formulas where L801A is defined]
bcs     LB757                   ; [BR if L00B3 < ($0CCD = 3277d) = RPM HIGHER THAN 300]

;                                … else [L00B3 >= ($0CCD = 3277d) = RPM LESS THAN OR EQUAL TO 300]
bclr    *L0038,#0x04            ; [Indicate [NO] DRP in 6.25ms [ISR] = NOT Enough RPM] for Start-up
clra                            ; A = 0
bra     LB78B                   ; BRANCH ALWAYS [Engine Turning Over to Start]

And here’s the math that hopefully supports that L801A (and thus L00B3) are “# of ECM Generated Reference Periods”:

; L801A:        .byte   0x0C,0xCD        ; Argument = $0CCD = 3277d = 300 START UP RPM
 
;
;       1 sec              1000000 Us               15.258789 Us Between (or per)
;   -----------------   x ----------------      = -------------------------------- = 1 ECM Reference Period
;   65536 ECM Pulses       1 sec                            1 ECM Pulse
;
;                             65536 ECM Pulses        60 sec               1 rev              1 min
;  ARG (# ECM Ref Periods) = ------------------ x  ------------      x   ------------  x  ----------------
;                                 sec                   min             4 DRP Pulses         X revs
;  Because the units of measure above all cancel prove the Argument is just a number = # of ECM Ref Periods
;
;           983040             983040
;   ARG = -----------      = ----------- = 3277 ECM Reference Periods
;            revs               300
;
;
;            revs         65536 ECM Pulses       60 sec         1 rev                1
;   RPM  = ----------- = ------------------- x ---------- x  --------------- x ---------------------------
;          1 minute         1 sec               1 minute       4 DRP Pulses      Arg (# ECM Ref Periods)
; 
;                  983040                     983040
;   RPM =  -------------------------     = ------------ = 300 RPM
;           Arg (# ECM Ref Periods)            3277

Seems confusing, but it clears things up for me. If anyone sees this differently, would appreciate your views.

[1project2many]

What appears to happen is the ECM reads the Distributor Pulses, converts them to ECM Pulses with a base frequency of 65536Hz and then outputs the equivalent ECM Reference Periods into variable L00B3.

The commenter of the ANHT hac (and others) often used his own shorthand and would mix references, likely due to familiarity with the material and systems. DRP Period is a correct term as it refers to the elapsed time, or period, between distributor reference pulses.

The ecm queries for the time between reference pulses as measured by the 65 kHz timer value then compares the result with the time value stored at $801A. The commenter did the conversion between time and RPM and listed the RPM in the comments. But that value onlyt represents 300 rpm for engines with eight cylinders.

Elsewhere in the code that same time variable is queried and the result is multiplied against the number of cylinders, or knumcyl. The result, now corrected for cylinder count, is saved as RPM. Engines with less than eight cylinders are corrected to eight cylinder values. The attached chart might serve as a handy lookup.

[84Elky]

The attached chart might serve as a handy lookup.

Exactly & Thanks! Where has this chart been all my life? The column labeled “cntr” (3^rd from right after adjusting the headings) is precisely the decimal value of what the code is getting from the ECM after the ECM receives DRPs at a given RPM. It’s the “# of ECM-generated Reference Periods at X RPM.

But believe the last column labeled “cntr * knumcyl” should be labeled (cntr * knumcyls) / 8, with no adjustment to “cntr” being required for 8 cyls.

Thanks again, and just curious about the origin of the chart and if there is other similar ECM related info available because have not seen this before?

[1project2many]

Exactly & Thanks! Where has this chart been all my life?

I made it back in 2000 when I was working through $58. I wrote a program to do the math in hex, with appropriate rounding, so I could see it happen step by step. I've posted it to a few sites over the years but the people that appreciate it are few and far between.

Why are you inserting "ECM generated reference periods" into the process? That phrase indicates the ecm is responsible for creating the value, which it is not. The ecm simply measures time between two events. No event, no measurement. Are you referring to the source of the value?

LDX L3FC0 ; LAST DRP PERIOD
STX L00B3 ; CURRENT MNR LOOP DRP PERIOD

I suppose this might be thought of as "Ecm generated" since the value is obtained from onboard hardware but it's the only "reference period" other than when "current" is moved to "old."

LDD L00B3 ; CURRENT MNR LOOP DRP PERIOD
STD L00B5 ; OLD REF PER

But believe the last column labeled “cntr * knumcyl” should be labeled (cntr * knumcyls) / 8, with no adjustment to “cntr” being required for 8 cyls.

The last column is the result of multiplication done by the ecm with the number of cylinders variable. There is no division. It's done with rounding. The time between DRP's is queried, knumcyl is loaded, and the two variables are sent to the standard 8X16 multiply subroutine.

CFAD            ldd     REFINT	
CFB0            std     rpmref	; L0037.  This will become 90deg ref * # of cylinders. 
CFB2            ldx     #0x0037	; places addy of rpmref in X
CFB5            ldaa    NUMCYL	; sets up for 8X16mult
CFB8            beq     LCFBF	; for 8cyl, goto LCFBF
CFBA            jsr     8X16mult	; generic multiply for 8X16 bit #'s: returns 16 bit 
					; value in D = 90 deg counter * NUMCYL
					;
CFBD            std     rpmref	; now we have a number = ref corrected for knumcyl

The logical tests are reversed in $8D (BNE vs BEQ) but the steps are the same. What's in the column is exactly what's generated by the 8X16 multiply subroutine for the listed counter and knumcyl values. If you're looking at this section:

LDD L00B3 ; CURRENT MNR LOOP DRP PERIOD
LSRD ; DIV BY 8
LSRD
LSRD

Its for dwell calculation.

What other info are you looking for?

Edit: The file I attached to the previous post was the raw data I obtained from the program. That's not what I intended to attach. This is formatted a little better.