On 03/15/2018 05:52 PM, Mia Magnusson wrote: > Den Thu, 15 Mar 2018 09:49:43 +0100 skrev Gerrit Heitsch > <gerrit@laosinh.s.bawue.de>: >> On 03/15/2018 09:21 AM, Baltissen, GJPAA (Ruud) wrote: >>> Hallo Patryk, >>> >>> >>>> No, it can't. PHI2 is nowhere to connect to there so it has to be >>>> taken care of externally. >>> >>> I meant: the moment you disable CS, the state of WE doesn't matter >>> anymore. In my designs I always make sure that PHI2 is part of CS >>> selection circuit. Using R/W could be dangerous: what if WE becomes >>> (H) before CS? In that case a bus clash can occur, even it is just >>> a very short time. >> >> In most systems you have bus clashes, but yes, short ones. Someone >> said that this is the reason why a 7501 uses less power than a 8501 >> (20mA less from, what I measured). The 8501 is faster, so it gets its >> lines active before the other side becomes inactive. > > The most important thing here is to study the data sheets / > specifications for the involved ICs to make sure that there is no harm > when a short bush clash occurs. With NMOS-drivers on both sides there can be no harm, that comes from the way NMOS and HMOS works. > You don't explicitly need to have a short bus clash for a fast bus to > work, it's just that it were probably easier to implement back in the > days. Back then the timing could change between different batches of the same chip... GerritReceived on 2018-03-15 19:06:11
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