This hardware trick keeps the injectors going even if the computer crashes.

It also greatly simplifies the PWM software.

I am thinking of implementing it on the ARM BASIC PC
board.

 Here is a picture of the  AD7203 DAC PC board layout.

The program places the pulse width digital data on the port and then
toggles the /WR  pin. Then the program or the CAS triggers the 555
injector driver. That is all there  is to it.

Very little processor overhead and no software bugs:) No timer interrupts.
You can  think of this as a glorified 555 fuel injector system.

As long as you  have power to it the CAS will keep triggering the injectors.

One of these years microcomputer chips makers will build these in like
they did with  my latched priority interrupts :)

Here is the final schematic.

We will see shorty how easy the ARM BASIC handles PWM.

Paul Lamar