Attached is the revised schematic -- the 74HC02 has been moved from U108 to U106 since the inverter has been removed.

For the memory map, this is what I'm thinking so far:

0000-7EFF: RAM
7F00-7FFF: I/O
8000-FFFF: ROM

and I'm thinking banks 01-05 would just be pure RAM.

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x86?  We ain't got no x86.  We don't NEED no stinking x86!

Check the direction of data flow through the 74AHCT245 - I think it's currently the wrong way round.

I would look more closely at your Reset device (MCP100-315).

1- This reset does not support a manual reset, so using a push-button switch will not cycle the delay sequence.
2- The datasheet shows that this device has a push-pull output. By shorting the output via the reset switch, you might damage the chip.

I suggest you look at an alternate device that has an open collector or open drain output. Also look for one that supports a manual reset.

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Regards, KM
https://github.com/floobydust

74AHCT245 would probably work, but the 74AHC245 (ie; the non- "T" version) would be a better choice. For starters, the "T" version is a 5 volt part (the datasheet recommends 4.5 to 5.5 V Vcc). And in this schematic the '245 and the '816 are powered at 3.3V (unless I'm missing something).

-- Jeff

_________________
In 1988 my 65C02 got six new registers and 44 new full-speed instructions!
https://laughtonelectronics.com/Arcana/ ... mmary.html

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x86?  We ain't got no x86.  We don't NEED no stinking x86!

As I've also been working towards a 3.3V design, I've researched quite a few piece parts for the first prototype. I'm not using a '245 for anything, however, I found some DIP parts that are 3.3V along with a 3.3V Reset chip and standard Radial half-size clock oscillator.

For the '245 data buffer, I suggest using a TI SN74LVC245A, which is a 3.3V part:


For the '573 latch, there's the TI SN74LVC573A, also a 3.3V part:


BTW, the DS-1813 is also a 5V part, so I would suggest using the Maxim DS-1233A:
(NOTE: the datasheet shows a 0.1uF cap in parallel with the reset switch.)


The Dual Flip-Flop should be okay.... has a voltage range down to 2V, but should consult the datasheet for slew rate at lower voltages.

Also, the default clock oscillator shown in a small SMT device (and 3.3V). Abracon make some 3.3V clock oscillators in half-size Radial sizes:


As always... consult the datasheet for everything.

_________________
Regards, KM
https://github.com/floobydust

_________________
x86?  We ain't got no x86.  We don't NEED no stinking x86!

That is certainly the trend, but the devices I attached datasheets for are available in DIP format and Mouser has stock as of right now. Also, the one's I listed do seem to have fairly fast response times. The LVC245 is spec'd at 6.3ns and the LVC573 is spec'd at 6.9ns, both at 3.3V.

_________________
Regards, KM
https://github.com/floobydust

The reason I've decided to use 3.3V is that I may in the future want to make an SPI/SD card addition to the board.

I also plan on having two 6522s, a real-time clock, and an LCD display using the ST7789VI driver/controller (https://www.newhavendisplay.com/resourc ... 7789Vi.pdf)

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http://WilsonMinesCo.com/ lots of 6502 resources
The "second front page" is http://wilsonminesco.com/links.html .
What's an additional VIA among friends, anyhow?

I found a few MCP100 datasheets online -- all from Microchip -- and they mention the push-pull output quite prominently (including a bullet point in the introductory list of Features and also in the document title itself, Microcontroller Supervisory Circuit with Push-Pull Output ). So unless you stumbled onto a less forthright datasheet from another manufacturer, I'm guessing you need to dial up the magnification on your PDF reader! Aren't you the one who's fond of saying, "The datasheet is your friend"? And did that detail about the AHCT part being 5 volt escape notice, too? Be that as it may, I wouldn't consider the MCP100's 3 mA output current even remotely insufficient for GamerFox's application.


Since the intent is to interrupt VCC, it's clear you mean a normally-closed pushbutton. So far so good, but unfortunately the pullup shown in the revised schematic might very possibly supply enough current to prevent /RESET from dropping to a valid logic low when the button is pushed.

A better suggestion for the MCP100 is one plasmo recently posted. The MCP100's VCC terminal would connect to the supply through a 1K or so current limiting resistor, and a normally-open pushbutton would, when pressed, shunt the VCC terminal to ground. Shown below are a pair of schematic excerpts altered to illustrate the two approaches. Instead of actually adding a 1K resistor, I "borrowed" a few of the unused 3.3Ks in the array.

-- Jeff

_________________
In 1988 my 65C02 got six new registers and 44 new full-speed instructions!
https://laughtonelectronics.com/Arcana/ ... mmary.html

_________________
x86?  We ain't got no x86.  We don't NEED no stinking x86!

Well, it's a relief to hear you're cheerful, because no offense was intended, and I'm certainly nothing but sympathetic for anyone facing a visual or other impairment. At the same time I think we would be straying from the topic if the impairment became the center of discussion. (I almost said, become the focus. ) In your posts you commonly include datasheet excerpts, and seem quite fluent, so we gather you're satisfactorily handy in accessing technical content -- which is great. I hope the wisecrack didn't distract from the point I was hoping to make about keeping well informed about the subject matter in one's posts.

-- Jeff

_________________
In 1988 my 65C02 got six new registers and 44 new full-speed instructions!
https://laughtonelectronics.com/Arcana/ ... mmary.html

Here's the new version of the sheet with the advice you gave me, and I'm a little afraid of cranking up phi2 too high to warrant memory bus ack lines.