On 6/4/2013 11:59 AM, Gerrit Heitsch wrote: > 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. My concern there is that it delays PHI2 all over, and it's typically the last signal to switch. I felt putting it through logic would create timing hazards. > > 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. That is an idea. I will look into that. > > 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. Well, I rant on cartridge designers who under-decode the IO address space, and thus it would be inconsistent for me to create a design that breaks my own passionate philosophy. > > > 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. That. I did not know. I will check that tonight. > > Maybe some of this is of use to you... No, all great ideas. I appreciate them. Jim > > Gerrit > > > > > > > > > Message was sent through the cbm-hackers mailing list -- Jim Brain email@example.com www.jbrain.com Message was sent through the cbm-hackers mailing listReceived on 2013-06-04 18:02:21
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