UK Vintage Radio Repair and Restoration Discussion Forum - View Single Post - Control-C, etc

TonyDuell · 14th Jun 2021, 5:12 am

Some time back I worked on a Computest unit, I mentioned it here. One puzzle I had was that the reset key (which like other machines of a similar vintage provides a hardware reset to the processor) seemed to do nothing.

It turned out there's a bit of logic on the keyboard PCB includng a monostable with a period of a couple of seconds. You have to hold the reset key down until the monostable times out for there to be a reset. Release it before that and nothing happens. This struck me as a rather neat way to protect against accidentally hitting the reset key.

14th Jun 2021, 5:12 am	#19
TonyDuell Dekatron Join Date: Jun 2015 Location: Biggin Hill, London, UK. Posts: 5,208	Re: Control-C, etc Some time back I worked on a Computest unit, I mentioned it here. One puzzle I had was that the reset key (which like other machines of a similar vintage provides a hardware reset to the processor) seemed to do nothing. It turned out there's a bit of logic on the keyboard PCB includng a monostable with a period of a couple of seconds. You have to hold the reset key down until the monostable times out for there to be a reset. Release it before that and nothing happens. This struck me as a rather neat way to protect against accidentally hitting the reset key.