I'm wondering what a bus cycle looks like for an operation like:

LDD #$7000;
STD L3FEA;

The timing peripheral chip is only 8 bits, and I'm not sure how the two bytes are written. Does it do two write cycles? What order do they write in?

I'm also wondering about the timing peripheral chip's PWM outputs. It seems like a 0% PWM is $7000 and 100% is $DFFF but I don't understand why those two numbers were picked, can any explain?

Can't wait until I get my test bench! Then all I'll need is a scope so I can see what's going on.

 

Uses two write cycles for the data to the peripheral device. Reg A goes first.

As for the PWM the high nibble in the data word is used to select the frequency. The low order nibbles are used for the duty cycle.

RBob.

 

Cool, thanks!

Is there documenation anywhere on the timing chip? I've been searching the diy-efi archives but I haven't had any luck. I'm wondering about what frequencies are available for PWM, but I don't want to keep bugging you guys.

Just in case anyone is wondering, a nibble is 4 bits, there are 2 nibbles in a byte.

 

Just so I have things straight.

From listings I found in ANHT
; 7000 = OFF
; D000 = O% DC
; D134 = 30% DC
; D200 = 50% DC
; DFFF = 100% DC

So $FFF is 100% and $D if some frequency?
If this is true, I don't get the math for %.

Or is it $DF & $FF?
Can't tell by how the nibbles were listed above.
But it makes more sense.
How do the freq #'s work?

 

A nibble is half a byte, or 4 bits. That refers to the $D value.

But you're right, the % listed doesn't make sense, when I divide $200 / $FFF, I get 0.125.

Unless $400 is the maximum DC and anything above that is 100%.

 

There is also a listing that $0066 increments the D.C. by 10%.
More to the mystery.
Still digging.

 

I may be off base on this one but I'll throw it out there.
Rbob's mention of the PW and DC being separate entites within the byte may be the answer here.
Controlling PW will give better "current" control while the DC is better for "banging" solenoids at full power (voltage controlled with no care for current requirements?). Control may have been setup to make additional smoothing of how the outputs operate with different devices.

DC = Amplitude, PW = Freq

 

$66 *3 =132
But the 50 and 100% values no where near track using $66 * 5 or 10.

Alex, I was hoping you'd scoped it by now.