[question] IC74HC595 as Input

[mohamedhamdiahmed]

Is it possible to use 74HC595 pins as input pins for limit switches and probe with ESP8266?

Also, can you please give a quick explanation of "Use board custom 74HC595 data shifter" option in HAL uCNC config builder (noob hobbyist, sorry)?

[Paciente8159]

No you cannot use 74HC595 as inputs. The 74HC595 is a serial to parallel shift register IC. You would need something that does the opposite like the 74HC165.

There is no current module for the 74HC165 (but the HAL is kind of prepared for that possibility). Also note that such device for homing and stuff might be limiting or suffer from imprecision (depending on the implementation).

About using the 74HC595 how many were you planning on using?

[mohamedhamdiahmed]

Thanks for the clarification.

I am planning to use 2 74HC595.

[Paciente8159]

To use 2 74HC595 the easiest way is to use the web builder.
You will need to assign 3 pins to control the 74hC595's.
You can then move almost all output pins to the 74HC595.

like in this example:

IO OFFSET(74HC595) pins 0 to 7 will correspond to the 8 pins in the 1st shifter and IO OFFSET(74HC595) 8-15 will correspond to the pins in the 2nd shifter.
In this example the step pins are the 1st 3 pins of the 1st shifter

The only pins you need to keep in the MCU IO are the 3 required pins to control the shifters and all hardware communication pins.

Here is an example:
I assign the ESP8266 GPIO 12, 13 and 14 to DOUT 47, 48 and 49

Then I enable 2 x 74HC595 shifters and assign the pins that will control them like this:

Note that some adjustments to the maximum step rate might be required to avoid the program from crashing like discussed here #812