On Mon, Apr 30, 2018 at 08:44:23PM +0200, Mia Magnusson wrote: > Den Mon, 30 Apr 2018 19:59:21 +0200 skrev Gerrit Heitsch > <gerrit@laosinh.s.bawue.de>: > > On 04/30/2018 07:51 PM, Mia Magnusson wrote: > > > But why not just join each of those TTL inputs with +5V directly on > > > the nearby chip? > > > > > > Does some 74xx IC's work better with slightly less drive to +5V on > > > the signal that feeds the inputs? > > > > I don't remember where, but I read somewhere, that you shouldn't > > connect a TTL input directly to +5V. > > Interesting! > > IIRC all data sheets indicate that anything between 2.4V and 5V is > treated like a correct "1". > > Maybe it's different on different TTL families? The B series uses a lot > of S logic. If you have a little bit of overvoltage on a TTL input (say, during power-on) you get a nice big fat short in the TTL device, taking out your power supply (or the whole system) if you have no current-limiting resistor on the input connected to Vcc. SegherReceived on 2018-05-01 02:00:03
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