Yet more progress! The monitor can now read intel hex records over the serial connection and verify the checksum. Combined with a "j" command that simply jumps to a location in memory, I can now theoretically load and run programs over serial.

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probably the youngest person on this forum

Excellent... Now, I have this TinyBasic you might want to play with

Cheers,

-Gordon

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--
Gordon Henderson.
See my Ruby 6502 and 65816 SBC projects here: https://projects.drogon.net/ruby/

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

You are technically correct. The best kind of correct.

It's happened surprisingly quickly - I expected writing the monitor to take hours and hours of debugging and poring over hex dumps, but it was pretty painless. In fact, the biggest error I found was with the code running on the AVR, not the 6502.

I'm not fully decided on where to go next - I might write a forth, while following along to https://colorforth.github.io/POL.htm.

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probably the youngest person on this forum

I'd also like to change how the monitor works a little - as is, it runs at about 8khz at full speed, which... isn't great. Unfortunately, with my current setup, I can't run the clock any faster (say, by using the AVR's timer to output a square wave on a pin) because I need to check the bus every cycle to perform serial operations. I can deal with it for now, but I'd like to have a proper freestanding UART at some point.

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probably the youngest person on this forum

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

Looks like my earlier maths was completely off, because I just doubled the AVR's clock speed (from 4mhz to 8mhz) and now it's clocking the 6502 at about 330khz. That's a much more acceptable speed, so I think I'll leave the monitor as it is for a while.

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probably the youngest person on this forum

No, I was just being stupid and forgot to reset the monitor before testing the speed. It seems closer to 60khz, which is still way better than 8.

And if I remove some unnecessary sleeps in the code, I can get it all the way up to 100khz. Result!

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probably the youngest person on this forum

I think my next goal will be talking to a character LCD I have (HD44780, of course). I'm currently thinking of using the 4-bit interface to save on IO pins.

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probably the youngest person on this forum

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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?

FYI - there are some really nice T6963C-based displays as well (most modern versions come with UCI6963, which is compatible with T6963C). You might need to cut some jumpers though to select a proper font, those are usually marked on display's PCB.
They have built-in fonts, graphic mode, come in sizes up to 240x128 (40*16 chars) and work at up to 5 MHz (5 times faster than HD44780). This allows them to be put directly on CPU bus without having to bit-bang (alternatively, you can use clock stretching circuits for slow LCDs - there have been some recent posts on this topic by gfoot, Jeff & myself over the past month). My Deck65 SBC uses one (240*64, 40*8 chars).

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/Andrew

deck65 - 6502 slab with screen and keyboard | ПК-88 - SBC based on KM1810VM88 (Ukrainian i8088 clone) | leo80 - simple Z80 SBC
nice65 - 6502 assembly linter | My parts, footprints & 3D models for KiCad/FreeCAD

Looking at it, I might just put it on the bus and use it in 8 bit mode. I only have one VIA, and port B is already reserved for SPI data in.

However I do it, physically connecting it will be very awkward, because the module I have just has an 8*2 pin header on, which I'm connecting to by jamming jumper wires into the other end of a ribbon cable. Some day I'll make a proper breakout for it, but today is not that day.

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probably the youngest person on this forum

And now the RAM has somehow exploded. This basically kills the computer because (as already mentioned earlier in the thread) the 62256s I have don't play nicely with the 6502 for whatever reason, and the 43256 worked for some reason.

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probably the youngest person on this forum

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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?