Hallo John, Sam, > Sam Laur writes: > And I wasn't going to waste > any time by using the simplest chips (74HC00), although that would have > a point too. It's just that then, a lot of time goes wasted, > constructing dozens of flipflops from NAND gates. I meant using TTL-chips from the whole ALS/LS/F-range as long as it is normally available. For example, I intend to use four 74LS191's as Program Counter. > Also the PLA should be easy-ish to make in discrete logic. How many people have an EPROM-programmer? And how many do have a PLA-programmer? > > >Instruction decode using an EPROM will be much easier, yes - but how > >complex would it be to make in hardcoded logic? Just give me the Boolean-equations and I'll build it. Some figures: every opcode can need up to 7 cycles. This means 8 plus 3 plus 1 bit for the clock. Then the needed cycles for some opcodes can vary: think for example of the branches. I reduced it to 1 bit. We need 1 bit to tell there is an Interrupt or Reset going on. This means that the Booelan equation of every outputline is calculated out of 14 inputs. Maybe as a little exercise: I'll use a 74ALS573 as Accu. Please calculate the boolean equation for outputting its data to the internal bus for all steps of every opcode :) > I think the main advantage of using an EPROM for complex logic is that > it can be changed very easily. No cutting tracks, soldering, and so on. > And it's very unlikely you'll get it perfectly right the first time. This was one of my reasons to choose for EPROMs as well. Another problem with PAL's are they are not re-usable. GAL's are but are expensive and need their own programmer as well. Groetjes, Ruud - This message was sent through the cbm-hackers mailing list. To unsubscribe: echo unsubscribe | mail firstname.lastname@example.org.
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