From looking at the schematic, the ESTOP is a signal TO the Due/Mega so that it knows the emergency stop button has been pushed.
The P302 connector is for connecting what appears to be a Normally Closed Emergency Stop switch. You press it, it locks open until physically reset (usually by turning it).
With P302 closed, the AND gates of the 74LS08 pass all the signals through. When P302 goes open (someone pushes the emergency stop) the signals are all blocked.
That said, I think there is a problem with this:
An 74LS08 (AND gate) is the wrong choice, as the motor enables are Active Low (you pull the signal low to enable). With the current setup, the enable signals for the motors will be ALWAYS low if the emergency stop is triggered, so nothing will actually stop.
We probably need to use a proper bus driver (eg: 74LS244), and then use pull-up/down resistors on the outputs to make the Z output state (ie: bus driver disabled) the default logic level required. Pull ups on motor enables, pull downs on FET outputs. Note also that an 74LS244 has 8 input/output pairs, so you'd only need one chip (not two, as proposed with the flawed 74LS08). It does add 8 resistors though.
The P302 connector is for connecting what appears to be a Normally Closed Emergency Stop switch. You press it, it locks open until physically reset (usually by turning it).
With P302 closed, the AND gates of the 74LS08 pass all the signals through. When P302 goes open (someone pushes the emergency stop) the signals are all blocked.
That said, I think there is a problem with this:
An 74LS08 (AND gate) is the wrong choice, as the motor enables are Active Low (you pull the signal low to enable). With the current setup, the enable signals for the motors will be ALWAYS low if the emergency stop is triggered, so nothing will actually stop.
We probably need to use a proper bus driver (eg: 74LS244), and then use pull-up/down resistors on the outputs to make the Z output state (ie: bus driver disabled) the default logic level required. Pull ups on motor enables, pull downs on FET outputs. Note also that an 74LS244 has 8 input/output pairs, so you'd only need one chip (not two, as proposed with the flawed 74LS08). It does add 8 resistors though.