On Mon, Apr 30, 2018 at 8:44 PM, Mia Magnusson <mia@plea.se> 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: >> > Den Mon, 30 Apr 2018 19:08:59 +0200 skrev Francesco Messineo >> > <francesco.messineo@gmail.com>: >> >> On Mon, Apr 30, 2018 at 7:05 PM, Mia Magnusson <mia@plea.se> wrote: >> >>> Den Mon, 30 Apr 2018 15:00:41 +0200 skrev Michał Pleban >> >>> <lists@michau.name>: >> >>>> Hello! >> >>>> >> >>>> Mia Magnusson wrote: >> >>>> >> >>>>> My intention is to find some kind of suitable software for >> >>>>> timing diagrams (I was first thinking about project management >> >>>>> software, but there seems to be software especially made for >> >>>>> thins purpose). >> >>>> >> >>>> Why not simply attaching a logic analyzer to various signals and >> >>>> measure what the real hardware does? >> >>> >> >>> Everything is made of standard 74xx circuits and standard DRAM's >> >>> (except the CPU and the CRTC) and it would be really nice to know >> >>> that the maximum and minimum delays is for each part of the >> >>> circuit. (The 6525's doesen't count in this discussion as their >> >>> timing isn't critical to understanding how the complicated >> >>> CPU-RAM-Refresh-Coprocessor stuff works). >> >>> >> >>> I wounder if anyone who designed or in general worked with the >> >>> hardware on theese machines at Commodore are still alive and >> >>> remembers some stuff? For example it would be nice to know why >> >>> some signals are called PUP1 and PUP2. >> >> >> >> look if they're static pulled up to some resistor to Vcc... >> >> PullUP1, PullUP2... Just guessing, but I use a similar naming >> >> scheme when I design my own boards. >> > >> > Thanks! Yes, they seem to go to pull-up resistors. >> > >> > 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. I always referred to: http://ecee.colorado.edu/~mcclurel/ON_Semiconductor_LSTTL_Data_DL121-D.pdf I used to connect TTL inputs (LS family, but I don't see why it should be different for S family) directly to VCC or GND when I didn't need to override the pull UP/DOWN. Using resistors maybe reduces the input current and lowers the power wasted, but max input current of LS/S families are in the tens of uA max.Received on 2018-04-30 23:00:03
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