On Saturday 10 June 2006 19:45, Peter Brett wrote: > 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 >
Yeah, probably. But my paranoia hadn't kicked in before then :) But the current setup will work (Assuming no stray commands on powerup or during a crash :). It just doesn't allow for the SPI PROM to be write protected. H
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