I have taken Kranenborg's frequency meter (itself based on an earlier design by Jeremy leach) and modified it to incorporate the LCD (or OLED - untested) display driver in the28X2 that's doing the frequency metering.
Port C is used for the display's 8 bit parallel data, B.0 is the ENABLE line and A.4 the RS. I expected some trouble because A.4 is also the Programming Serial Out pin but I found that programming is still possible even with A.4 connected to an LCD's RS input.
The attached program includes a description of the basic circuit.
There is also an input signal conditioning circuit but that has been disappointing - it only works over 1kHz-300kHz although with direct input the meter works up to at least 4MHz. I don't have equipment to test higher frequencies - the frequency meter should work at up to 65MHz. I am self-taught in electronics so feel free to suggest improvements to the circuit.
Port C is used for the display's 8 bit parallel data, B.0 is the ENABLE line and A.4 the RS. I expected some trouble because A.4 is also the Programming Serial Out pin but I found that programming is still possible even with A.4 connected to an LCD's RS input.
The attached program includes a description of the basic circuit.
There is also an input signal conditioning circuit but that has been disappointing - it only works over 1kHz-300kHz although with direct input the meter works up to at least 4MHz. I don't have equipment to test higher frequencies - the frequency meter should work at up to 65MHz. I am self-taught in electronics so feel free to suggest improvements to the circuit.