Kevin,
I got it working. What threw me for awhile is the /WR pin on the DAC >>>MUST<<< be
toggled for the output of the DAC to change. Here is a picture of the AD7203 DAC set
up with dip sw input for testing. Here is the final schematic.

The program places the pulse width digital data on the port and then toggles the /WR
pin. Then the program 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.

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


Paul Lamar


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