fachat wrote:
You've left out some parts of the schematics I think. I am wondering, do you have any more RDY logic or do you run all parts with CPU clock speed?
Everything is running at the MPU clock speed in this first design. I'll initially bring it up on 1 MHz (2 MHz oscillator) to verify that it's upright with a pulse. Assuming it gets through that, I'll ramp up the clock rate until something messes up. Most likely, the speed limiter will be the DS1511 timekeeper. The EPROM is rated at 70ns and the SRAM at 12ns, so I don't expect that they'll be a concern. Past experience with Dallas Semi's timekeepers, however, indicates that they are quite slow, especially during write ops.
Once this design is working I'll develop another design that can wait-state peripheral access. On that unit, I'll try running the clock speed up to the max to see what happens.
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A naming thing: WD and /WD are named as if one is the inverted signal of the other - but /WD is qualified by Phi2, while WD is not. I found such naming to easily be source of problems when you just mess them up, or you later need a real inverted version of one of those signals.
I agree the naming could be a bit confusing. The WD signal is an inversion of the MPU's RWB. WD, as you probably noted, is used to gate output enable on memory or I/O. So, disregarding the Ø2 qualification applied to /WD, WD is the inversion of /WD. Perhaps I should rename WD to /RWB.
![Smile :)](./images/smilies/icon_smile.gif)
Quote:
Looking forward to your results!
André
It will all be posted here, good or not-so-good.
![Smile :)](./images/smilies/icon_smile.gif)
I will have some pictures of the board as I populate it, as well as some 'scope shots if I see life after applying power. Assuming the unit doesn't fill up my shop with nasty-smelling smoke and activity is present on the address and data lines, I will then connect one of my old WYSE 60 terminals to EIA-232 port A. Following reset, code in the EPROM should write some text to the terminal screen and spin in an input loop looking for some keyboard input.
As I said when I started this topic, I've worked with this stuff literally for decades but have never scratch-designed and built a computer (excepting a relay computer I built while in high school). This
Proof
Of
Concept design will mostly prove that I know what I'm doing...or not!