On Saturday 10 June 2006 19:00, Hamish wrote: > On Saturday 10 June 2006 18:37, Peter Brett wrote: > > Okay, I had a closer look at the schematics & the PROM datasheet, and I > > see what's going on. I would have tied the !CE pin high with a 4.7K > > pull-up to minimize any chance of junk signals being accepted by the PROM > > during board power-up, but it doesn't look like Howard's done that. I > > assume that's by deliberate choice. :) > > It's been a long long while since I did any of that... But from memory we > only used to connect via a pull-up resistor on logic if we wanted to > connect an input to an output AND have a... default... (Maybe my words are > wrong).
No, power-up considerations are important too. I think it's best to make sure that as the rails come up the pins go to a sensible default. > But I would have thought, connect WP_ to GND with a resistor and then also > direct to a tristate output of XP6... Then if you don't drive XP6 output, > the chip is write protected. Otherwise if you drive the XP6 output HIGH > (i.e. Vcc) the chip is NOT write-protected. Hmm... it depends on the behaviour of the XP6's IOs before and during configuration, but that doesn't sound unreasonable. Should have had this conversation _before_ they did the artwork, really. :P Peter -- Quake II build tools maintainer http://tinyurl.com/fkldd v2sw6YShw7$ln5pr6ck3ma8u6/8Lw3+2m0l7Ci6e4+8t4Eb8Aen5+6g6Pa2Xs5MSr5p4 hackerkey.com
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