On 06/04/2013 04:14 AM, Jim Brain wrote: > As I look at it, I can;t help but wonder if some juggling of the address > lines and such would simplify things and remove the requirement for an > inverter altogether, but I am not seeing an easy way to do it. > > http://jbrain.com/vicug/gallery/vicmidi/VIC_MIDI_Schematic You have a few unused inputs on the LS688. Can't you use them to include PHI2 into the _SEL signal already? That would mean you could free up some inputs on the other logic simplify the circuit there. Like this: Hook up PHI2 to Q6 and tie P6 high. Then the _SEL signal will already include PHI2 and you no longer need it at the UART. Also why do you hook up CR/_W to the 74LS138? You could use that on G2 of the 74LS173. Hm, if you're willing to use _IO2 completly, you could get rid of the LS688 and use the LS138 to decode the I/O-Space for the UART and Banking register. It has a high active input, meaning you could add PHI2 here as well. Then you should read the datasheet for the Flash since for most RAMs, _WE overrides _OE, meaning you can tie _CE and _OE together. If that's the same for the flash, you can free up an inverter for use elsewhere. Maybe some of this is of use to you... Gerrit Message was sent through the cbm-hackers mailing listReceived on 2013-06-04 18:00:11
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