6502.org

I have a fistful of 68B50 UARTs, which are nominally 2MHz parts. I can use the same clock signal for TXck, RXck, and E (motorola's version of ph2) and division by 16 gives a 115,200 baud rate. Simple. I like it because it's a basic parallel databus interface without the complexities of the intel parallel parts. So a very simple design...

Project goals have not been formally stated as I spent far too long being constrained as or by project managers! The basic idea is whatever seems to be a good idea at the time... but as a minimum, I want to be able to read a (named) file from the CF in a vaguely efficient way; follow that with writing. That way I can have a transfer medium compatible with my linux box.

Eventually, we might envisage a variant on this design to have most of 64k as RAM, with a couple of K or less of rom which basically has the DOS in it and can talk to the disc. A basic OS can be downloaded from the disc and overwritten by active programs, also taken from disc. Think early MSDOS or CP/M.

Things I would like to have are a self-hosted assembler, an extension to my tiny basic to store on the disc, and in particular a text editor that can handle files significantly larger than the available memory. Output will either be to an external terminal, or perhaps, if I can get it working, to VGA using a pi pico.

Might keep me busy for a while.

Neil

Thanks Chad. I find that the SOP-28 parts for both ram and eeprom are significantly cheaper than the DIP packages, and once I worked out how to do it it's a no-brainer to apply both feetprints if if makes sense (e.g. if you're not going to be programming the eeprom in situ, you may as well use the dip as it's going to be in and out of the board for development).

To do this trick with Kicad, set a DIP package in the schematic layout and place that on the PCB layout. Then select 'place footprint' from the menu or the icon group, and select an SOP-28. It will fit in inside the standard DIP socket with round pins (not the long pins) but you will need to select the grid to (I think) 0.635mm, possibly 0.3175mm, to get everything lined up without touching. Centre the SOP on the same point as the DIP and it will fit.

Then you need to double click every pin on the SOP in sequence, and select the net name to be the same as the same pin on the DIP, which will make the ratsnest join the pins together. Neil

Thank you for that. I had never used that particular feature. I would have probably edited the existing footprint in its own separate window, added a SO-28 footprint with pads, save as a custom footprint, then point to that new footprint in the schematics. Good for future use, but a pain to go through the process! Nevertheless, what you have looks beautiful, and useful.
Neat! So now I see you and Bill (plasmo) both using this CF card, it must be a good way to transfer data? I'm very used to using the MicroSD cards at this point, but usually I use a little 5V -> 3V3 adapter to interface with it. Still, that is very slow in comparison to the CF card, which I'm guessing runs in parallel?

Good goals, would definitely like seeing updates on this. Are you going to use a different topic, or do you already have another topic for this board open already?

Chad

Progress to date has been noted here: viewtopic.php?f=4&t=8482 but I think I shall start a new FAT32 thread fairly soon.

Neil