OK, I'll research this and see what I can come up with.

I like this approach!

Either approach sounds good to me. So SW1 resets the FPGA I take it?

I get it. It would be low on my list too, except that I'd like to have support for a USB or PS/2 keyboard. What are your thoughts on supporting keyboards?

Oh, one more suggestion. Consider putting vias or test points on the unconnected pins of the 65C02/65C816 to make it easier to connect to them should a use be discovered for them in the future.

It starts a new configuration cycle, so it loads everything from flash, and starts running. During the initialization, the FPGA resets the CPU. However, it will also restart all the other peripherals, and clear the internal memory, so not necessarily always what you want.


As far as I know, most keyboards will accept PS/2 protocol on their USB connector. That should be simple to implement, so we can start with that. Implementing a USB host, plus HID layer would be a bit more complicated. Still, a USB keyboard is a relatively simple device, as far as USB devices go.

However, trapping with NMI causes the MPU to resume on the next instruction, whereas trapping with ABORT causes the MPU to re-execute the same instruction. The reasoning has to do with ABORT's use for managing a virtual memory environment.

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

Was there ever a commercial or otherwise well-known VM OS for the 65816?

True, but for the purpose of trapping memory access violations or privileged instructions, that shouldn't matter much. It would be useful for virtual memory, but with up to 64MB RAM on board, a VM system wouldn't add much.

I'm not aware of one, although the Apple ][gs may have had some elements of it in its OS.

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

I've seen quite a few members of various hobby sites running into keyboards which won't work with PS/2. It looks like these days the PS/2 compatibility is not always included.

-Tor

Got video routed (except for 1.8V LDO and I2C, but those are easy). Lots of tight spots I decided to implement VGA using 4 resistors (499R, 1K, 2K, and 4.02K). That's good enough for our purposes, and these resistor values are still fairly common.

J6 is the VGA connector, and J7 is the PAL/NTSC connector, implemented using 3.5 mm three-ring jack.

My plans for the connector layout - on the back: VGA, TV, Audio and mini USB power in. On the right: USB, uSD card, UART and extension header. I'll probably shift the VGA connector to the left, and make the board slightly longer on the right. Probably 9x8 cm, or maybe even 10x8 cm.

Arlet, please have a look at these parts for the power supply:

http://search.murata.co.jp/Ceramy/image/img/A14X/2HN_E.pdf

They are tiny self-contained modules with DC-DC converters on them not much larger than a linear converter like the one you are using. Prices are about the same as the linear regulators too. Maximum current is 600 mA for these, though if that's not enough there are larger modules available too. Digikey carries these, so I imagine they are easy to get from many suppliers.

You'd need three of them -- one for each output voltage required.

If the 4-SMD package is a problem to solder, Altera and TI make similar (but more expensive) parts in QFN-14 and LLP-8 packaging with exposed pads. However, I have hand-soldered other 4-SMD packages before and found it not too difficult. And if you're planning on reflowing the boards, it certainly won't be an issue at all.

These DC/DC converters are very nice, but Digi-Key only has the 3.3V in stock. Farnell doesn't have any of them. Mouser doesn't have the 1.2V in stock either.

These are slightly more expensive, but are programmable so you don't have to worry about picking up different parts for different voltages:

http://www.ti.com/lit/ds/symlink/lmz10500.pdf

Additionally, the Altera parts are another option too:

https://www.altera.com/content/dam/altera-www/global/en_US/pdfs/literature/ds/ep5348ui_05721.pdf

Both of the above are in-stock at Digikey now.

Going directly for USB is an option too. It's not really all that complicated, provided the 6502 can do the higher level functions, such as configuration. After that, it's just a matter of repeatedly sending the same packet every millisecond. If the reply contains data, store it in memory, and interrupt the CPU. Otherwise, ignore it.