In fact it's my question :) aging synertek 6502 or strange 6502 from synertek for the low level I've not noticed anything special they all looked slightly above 0, the same for all 6502 tested I'm connecting the 6502 bus to a 3.3v chip with 1k resistors... (a propeller) not sure if the signal would still be ok after the 5v to 3.3v conversion if the high level is at 2.5v the goal of the propeller is to catch the write between $8000 and $8fff and produce a video signal on vga I'm retrying the tests of my board after having replaced the synertek 6502 by a mos 6502 On 05/11/2016 22:01, Francesco Messineo wrote: > On Sat, Nov 5, 2016 at 9:56 PM, didier derny <didier@aida.org> wrote: >> Hi >> >> the 65c02 high level was near VCC >> >> I had 2 Synertek 6502 both were at 2.5v for the high level... >> >> 2 differents machines SYM1 and CBM8032, same results... >> >> looks like the problem is linked to the synertek > the High voltage at 2.5V isn't a problem in itself (if it keeps the > level when loaded). TTL logic real "bad" noise margin is on the low > level (0.5V max output vs 0.8V max input). > So in theory 2.5V High should work as it has a still better noise > margin than the correct Low levels. Look also at the actual Low level > voltages on these parts however. > Then, one might wonder if Synertek parts were always marginal or they > didn't age well, but I can't surely tell :) > >> >> >> On 05/11/2016 21:50, Francesco Messineo wrote: >>> On Sat, Nov 5, 2016 at 9:37 PM, didier derny <didier@aida.org> wrote: >>>> while checking some signals on the 6502 of my 8032 motherboard >>>> I found the 'high' level rather low 2.5v (I expected around 4v...) >>>> >>>> so I took my SYM1 board and tested several 6502 >>>> MOS 6502 around 4v >>>> Rockwell 6502 around 4v >>>> Rockwell 65c02 around 5v >>>> Synertek 6502 around 2.5v >>>> CM630 around 4v (bulgarian clone) >>>> >>>> I tried several 6502 of each type... >>> >>> 2.5V is really a bit outside the acceptable output High level for TTL >>> logic. >>> 2.7V is the official minimum level for the High state. However, TTL >>> inputs should accept as High any voltage => 2V. >>> If the current capability of the outputs isn't degraded (i.e. if 2.5V >>> is maintained at all the inputs when loaded at the max fan-out), I'd >>> say it should still work. >>> CMOS outputs, on the other hand, should go to the power rails, if they >>> aren't broken. >>> Do you have many Synertek and they all have the same output levels? >>> >>> Frank >>> >>> Message was sent through the cbm-hackers mailing list >> >> >> Message was sent through the cbm-hackers mailing list > Message was sent through the cbm-hackers mailing list Message was sent through the cbm-hackers mailing listReceived on 2016-11-05 22:00:22
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