For future reference...all of the issues I had were caused from enabling the FIFO. I didn't realize that by leaving the FIFO disabled it would work character-at-a-time.

Now that the issue is resolved, I guess it's on to learn how to program for the FIFO

I know that the forum is mostly agreed that newer UART solutions are better, but I'm constrained at the moment by what I have available, which is a NXP PC16550DV :) Here's it's datasheet :

I've connected the 16550 much like this example with some chip selection differences (CS0 and CS1 tied to +5v ...

Well, progress is being made! I've got a simple breadboard set up with a 6551 and a 6522 for testing purposes. Since I'm still using the QXB board, I removed the resistor packs across the port 7 LEDs and soldered to CS0, CS3, and CS4. SRAM and flash work just fine, but I'm having some trouble ...

The '265 is able to run with clocks up to about 8Mhz by itself, as the internal ROM monitor is ready to accept that frequencies and configure the serial ports connected to USB.

I managed to get it working connected to the expansion port of a Commodore 64, the outputs a clock signal of ~8mhz ...

Looks like I was too quick to write. @tokafondo has made the point here that the ROM can't be disabled. Oh well.

Given that, I guess I can get the system going with the WDC string in the ROM. Now to see how fast I can push the thing, given I am limited on how fast the chip can start up...

I'm glad to see some thoughts here...it's good to see that people have opinions. I'm still forming my own regarding this MCU. :D The reason I decided to use it is because I had some unloved SBX boards here, and I wanted to see what it was capable of. Sadly, 3.68MHz is not enough to read the bits ...

Just to close the loop here...I was shown that the things I am seeing are expected. The USB serial isn't a separate UART...it is using port 5 and 6. Port 4 also controls /RESET, which I disabled.

My goal was to have a one-chip solution like the Arduino or ESP32, but I can't find enough free pins ...

I'm feeling a little frustrated at the moment, so please take any rants as unintentional...

I've been trying to use one of the 265SXB boards as a floppy controller, and while I am getting some success, there also seems to be some peculiar things happening along the way. I'm hoping that the people ...

Okay, I've done a bit more study of the datasheets for the 265sxb and the '265 itself. I can see that J4 and J5 are the UARTs (when enabled) and just plain pins (P50-P57, P60-P67) when disabled.) If I keep these pins disabled, including the special interrupt functions for P56, P60, and P62, can ...

I'm wanting to use the 265SXB that I've bought for something more useful than blinking LEDs, and so I've decided to build a floppy controller from it.

Background: My son and I both acquired Kaypro IIs, and no way to write new disks. If I had an older DOS machine it would be simple, but eBay ...

Hi Garth,

Thanks for your thoughts...I hadn't really gotten to optimizations yet for two reasons: I've built a target with SyMon, which only supports NMOS 6502 instructions; and I haven't really looked at the 65c02 instructions yet, as I come from assembly with my trusty C64 and C128. I just wanted ...

Ed, you're a genius! I replaced D0 and D1 and it works a charm Thanks!

Ed,

Its all on a breadboard...and all run through a single 1.8MHz oscillator. It sounds like you are saying that D0 might be bad?

I remember purchasing the toolkit when it was $40...but I've lost the binaries. I wonder if they'll replace it since it was a purchased copy...

I'm having some serial issues, and I'm not quite sure where to go with it.

I've attached two pictures -- one expected output, and one actual output. I've tried changing baud rates and from a WDC 65c51 to a Rockwell 65C51, and both exhibit the same behavior. I don't have another MAX233 to try, but ...