This is one example of why I designed the 65SPI interface. It provides a serial bus between the 6502 and peripherals such as PIC's and AVR's.

For a simple parallel interface, you need two 8-bit latches that the 6502 writes to and the peripheral reads. One provides a data byte, the other are handshake bits from 6502 to peripheral. You will also need two 8 bit latches that the peripheral can write to and the 6502 reads - one for data and one for handshake. Then, its just a matter using firmware on both sides to control data flow.

EhBASIC would then use that firmware to check for incoming keystrokes and send outgoing data bytes.

In any bus system, you need to define a physical layer - the actual wires connecting the bus, and the logical layer - the firmware that controls the physical layer and provides the interface protocol.

Since you are wanting to access mutliple features, your protocol will have to include how to handle that.

My SBC-3 has an AVR device off of the 65SPI that reads the keyboard and provides a two-way RS-232 channel. You can dig through my source code to see how I handles that. It wasn't easy to ensure no data got lost or repeated, but I was able to come up with a system that works.

http://sbc.rictor.org/

Hope this help!


Daryl

Yes, I think Daryl's 65SPI chip could give you more interfacing overall for the number of connections used, which is important when you consider the amount of time needed to make your own home-made setup. In fact, part of the 65SIB (serial interface bus, related to but not to be confused with the 65SPI chip) was to include specifications on how to use something like a PIC microcontroller for exactly what you're talking about doing, but we never got that defined. Samuel Falvo was going to do the portion of the specification relating to autoconfiguration. I might still make PICs available to act as hubs to have sub-buses to get past the 7-slave limitation. The basic specification of 65SIB however is at viewtopic.php?t=1064&start=105 . Daryl's 65SPI IC info is available at http://sbc.rictor.org/65spi.html.

If you do the PIC parallel slave port (PSP) though, and make it a master-slave setup instead of peer-to-peer, you can interface the PIC to a 65xx system through a single bi-directional port (PA or PB) of a 6522 VIA. Each port has both an input register and an output register. Without drawing it up right now to figure it out, I expect CA1/CA2 or CB1/CB2 will give all the extra hardware support lines needed. Edit, 10/19/18: Microchip's ap. note AN579, about using the PSP, is at http://ww1.microchip.com/downloads/en/A ... 00579b.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?

Well i wrote a basic program for the pic (didn't solder the socket for it yet, ill post my progress within a few days), for now it will only be able to output pressed ascii characters on the psp, and write to the lcd through the psp.
Other functions like i2c and a/d i thought about putting two additional latches one input one output, so that keyboard and display are separate from the i2c, a/d, and mouse...

Darryl, just a thought, what do you think of splitting off the keyboard/RS232 as its own project to place on here so others may use your work in theirs?

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"My biggest dream in life? Building black plywood Habitrails"

When i finish this. I will make the code kinda modular, so it can be taken apart easily...

I may be able to get that done. On SBC-3, I did cheat and use one extra handshake line outside of the SPI bus. It ran beween the AVR and a VIA input. Will see if I can clean that up so it's a pure SPI interface.

I cannot promise anything in the near future however.

Daryl

it writes characters on the lcd!

After 4 hours i managed to write "Hello World!" on the lcd, because i placed the string on the wrong address and the 6502 would echo junk from ram...
I already thought that there is something verry wrong with my project, then i remembered about the address trick(in the simulator the program is located on $0000, but on the sbc is on the $C000)...
I still need to test what is the max writing speed...

I wanted to post the picture of the sbc in action, but ms paint will not open
pictures taken from windows phone7 (OMG)...
So here is the link if you want to take a look
http://www.iteracija.com/mupload/hw.jpg

Great! So, from the 6502 side, this looks like a simple output port, which you write the characters 'H' 'e' 'l' and so on, and the PIC acts like a teletype?

Yes! Since i use the psp interrupt to get pics attention, i will now make a buffer, so it will be able to read characters at higher speeds...

Now i managed to get working the keyboard interface part.

I think the keyboard interface part is finished, except for small bug where Z turns into Y when holding shift... Now i can go to the mouse and RTC part...

While i was thinking about how the Altair8800 had may lights for addresses/data and about the 6502 debugging whit low clock speed, i got this idea: Why not use this pic for debugging, it just needs the sync and clock signal, and then it could decode assembly instructions and print them on the lcd as you step through the program...