Hi I’m in the middle of setting up a new circuit for my st7920 display, I have a few questions about the correct way to do things. Any advice is helpful.
1.
My first design ran 2 x 74HC595 + ST7920 all off the 5v pin, are logic chips enough to warrant me using a power supply, I’m adding a 74HC165N ( PISO Register ), a 74HC04N ( Hex inverter ), and a 74HC51B1 ( AND/OR invert gate ).
They are only driving arduino pins and a shift register OE pin, what I would consider small loads, but not sure.
The datasheet for the Hex inverter says to attach each unused input to Vcc or GND for correct operation. Is this a general rule to follow for other logic chips?
The LCD data lines are connected to the 74HC595 register for write mode, and are also connected to the 74HC165N inputs. Will the input register stop the output register from sending data correctly? Resistors on input register maybe? Or are the 165’s inputs not connected until the shift/load (SH/LD) is taken low.
For read mode, the other logic chips trigger the output enable on the output register switching to tri-state mode. Is this suitable to allow the input register to read the data or is some additional protection required?
Cheers