I'm trying to make a unit in which 4 digits can be updated in a small amount of time from a single-cycle microcontroller (preferably all digits updated within 5uS)
My circuit is setup in the following way, (I excluded 7 segment displays and resistors for simplicity). The shift registers are 74HC595 and the multivibrator on left is the CD4538 but I think I need to upgrade that to 74HC4538 (someone confirm this?)
I have a multivibrator because the shift registers need the register clock toggled to display the new data that is shifted in, so by adding one, I eliminated a need of a 3rd wire from the micro that only updates the value.
The resistor is 10K and the capacitor is 1nF.
If I use a lower speed micro like the AT89S52 that can only update GPIO pins at best of 1/2 a microsecond (with 22Mhz crystal), then this circuit has no problem. But if I start to use the high speed single-cycle microcontroller, then GPIO pins could update as fast as 20nS.
What can I do to improve this circuit without rearranging parts? Should I just upgrade the multivibrator and lower capacitor value?