Sounds like a fun project...

From your initial post, I'm thinking what you've done so far would be closer to creating a BIOS for the hardware. Do you have a hardware design in mind? Just trying to understand what you're creating.

As for monitors, I think you can likely find many examples out ...

I believe the boxes represent some buffers/latches, like the 74LS244 and the upper being bidirectional like the 74LS245.

As for the basic circuit block level, it looks fairly high level. You'll also need a dot clock to drive the shift register (74LS166 ?) and the rest of the circuitry to provide ...

Yes, not my file... just grabbed PDF from RC2014 site some years ago.

Try this:

Just an thought... the RC2014 Bus project has a 512KB RAM/ROM card which uses a pair of the '670 register chips.

There's also the Fuzix project that supports the memory expansion and has a 65C02 port as well as the normal Z80 CPU used on the RC2014 series of boards.

Attached the PDF schematic ...

Oddly, I was wondering if BillO was using the 6551 chips in polled mode only, i.e., no interrupt driven receive or transmit. I only use the 65(C)51 in interrupt driven mode and I've not been able to ramp the chips up to the high clock rates that BillO has gotten with his setup.

Per the OP,

I've been using interrupt-driven code for years on my C02 Pocket SBC for the serial port and also a jiffy clock with the NXP (D)UARTs which includes a timer. I also implement 128-byte circular buffers for the serial port (used as a console) with RTS/CTS handshaking.

I also have used ...

All,

I finally completed a new DOS/65 release... 3.21. Quite a bit of changes since the 3.20 release. I also did a new C02 BIOS V5 and an updated hardware spec in the process. It's on my GitHub page, but I've also included the two directory structures here in a ZIP file.

If anyone decides to ...

Yes, that was the last version I worked on. I just checked my GitHub page and it's not there, just the previous P4 version. At some point, I'll update that.

Well, Happy New to the forum as well... and I'm actually able to access it while I'm in GA for the holidays.

As Garth noted, things tends to change over time. I've been more busy doing house projects, some car stuff and back into my audio gear for a change. This is now just gearing up (I guess pun ...

Just a quick follow-up, here's some links to find some of the code I referenced in my initial post:

Dietrich's CPM-65:
https://github.com/Dietrich-L/CPM-65

David Given's CPM65:
https://github.com/davidgiven/cpm65

Rich Leary's DOS/65:
http://retro.hansotten.nl/6502-sbc/dos-65/

Fuzix:
https ...

I want to create a small OS with bare metal CLI. What should I do?

That's a difficult question. First, have you searched around to see what's already been done in this area for the 6502? There are already several small OS type environments available. They include Dieter's CPM65, Rich Leary's DOS ...

Yes, the FIFO can be a different thing. I've not written any support routines for the 16550, but dabbled with the 8250 and 16450 back in the 80's...

Some years ago, I ditched the 6551 and started with the SCC2691 and later to the SC28L92 DUART. I also found coding for the FIFO a bit interesting ...

Most interesting... is there a version of Flex that I could try to port to my 65C02 system? I'm now using a RAM based DOS/65 version that boots from an IDE drive. There is currently 56KB of contiguous RAM.

Here's one I liked, but the OP has basically vanished since his only thread:

viewtopic.php?f=4&t=6888&p=88756&hilit=fuzix#p88756

I'm still hoping to build up a much smaller (65C02) system that will run Fuzix at some point...

I built up one of Bill's original CRC65 boards... and it's running as a UART at 115,200 N-8-1 via a USB/UART adapter. Perhaps looks at the build files... which requires the older Quartus II tooling.