English Amiga Board - View Single Post - Two input, Single Output

Daedalus · 19 May 2018, 23:32

Yeah, there was a common design doing the rounds a little while back that had issues due to the lack of pull-ups. I'm sure it works fine under certain tests, but TTL inputs should not be left floating as any noise from nearby cables (or even joystick or mouse movements) could trigger it. An issue could also be if the PS/2 adaptor uses signals that are open collector, or incompatible with TTL or whatever logic family is used for the switch. In these cases, a pull-up resistor should also help things along.

19 May 2018, 23:32	#8
Daedalus Registered User Join Date: Jun 2009 Location: Dublin, then Glasgow Posts: 6,374	Yeah, there was a common design doing the rounds a little while back that had issues due to the lack of pull-ups. I'm sure it works fine under certain tests, but TTL inputs should not be left floating as any noise from nearby cables (or even joystick or mouse movements) could trigger it. An issue could also be if the PS/2 adaptor uses signals that are open collector, or incompatible with TTL or whatever logic family is used for the switch. In these cases, a pull-up resistor should also help things along.