Hi, according to the datasheets, HCT08 is a few ns SLOWER than an LS08. Are all unused inputs of the '08 tied to a supply rail? HTH Frank IZ8DWF On Wed, Aug 9, 2017 at 6:49 AM, Jim Brain <firstname.lastname@example.org> wrote: > Trying to help some folks with issues related to an EasyFlash-derived > design, I have been debugging the circuit and I'm momentarily stumped on the > issue. > > The design is exactly the same as the stock EF1 design, with 1 change. > Instead of 2 FLASH ROMs (one in $8000 and one at $a000), I put a single > FLASH ROM on the PCB and wired ROMH and ROML through a 74'08 to !CE > With all HCT parts, the unit will not flash on non 250469 boards. > With all HCT parts but the '08 (74ls08), the same unit will flash correctly > on non 250469 boards (at least a few I have tried). > > SO, my hyposthesis was that the ROMH and ROML signals need some settling > time before being applied to !CE. > > However, when I remove the '08 from the circuit and hardwire the !CE line of > the FLASH ROM to ROML, the unit works on non 250469 boards. That would > indicate either 1 of two things: > > Faster than HCT (no latency) is required (or lots of LS latency) > The interaction of the ROMH and ROML signals is causing glitches. > > I don't see the glitches yet, but I continue to test. What I wonder is how > other systems handled sharing a ROM between ROMH and ROML. THe '08 seemed a > logical choice (no pun intended), but possibly some other idea is better. I > tried gating the CE signal with PHI2, but that did not help. > > Any thoughts are appreciated. > > Jim > > -- > Jim Brain > email@example.com > www.jbrain.com Message was sent through the cbm-hackers mailing listReceived on 2017-08-09 08:00:07
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