Hello,
I am wondering if there are any differences between the 6850 and the 6551 when you look at it from the CPU's point of view?
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Well, never mind. The 6850 has only one register select lines and the 6551 has two. What I would have liked to do is make a batch (1-10) of rs232 cardriges for the c64/128. I want to get my terminal on...

The 6551 is easier to interface to the C-64/C-128 cartridge port than the 6850. This is one of the few situations where I would recommend use of the 6551.

That said, your choices of UARTs are not limited to the 6551 or 6850. Modern UARTs aren't too difficult to interface and offers advantages over the old stuff. It sounds as though you are contemplating building these cartridges for sale. I'd carefully think this through.

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

GhstWlf, welcome back! You haven't posted in years! We'd be interested to know what happened with your project of making an '816-based laptop similar to the TRS-80 model 100.

The C64 and C128 run slowly enough that any version of the '51 would keep up, so you don't need the WDC one if you have (or can get) older ones. The WDC one has the bug of the transmit-register-empty flag stuck, so you have to make sure your software gives enough time for the ACIA to send a byte before you feed it another and lose one. I have been using CMOS 51's (65c51's) from Rockwell and CMD for the last 25 years and have never had any trouble with them, although it would have been nice if the control for a couple of different things had not been merged into one bit. (I suppose the designers were trying to stay down to four registers and avoid adding another RS pin.) The NMOS '51 does have what I would consider either a serious bug or a really idiotic design; so I would avoid the NMOS. That said, the '51 does have an onboard baud-rate generator, unlike the 6850, and, if you want oddball or faster rates, you can still select to use an external clock, which I have done for MIDI which runs at 31.25kbps.

There's plenty more here in the forum archives about the '51 ACIA and other UARTs, so do a search.

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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?

I have a cartridge port UART card that I designed for the C-128 that was built around the NXP 2692, with both ports brought out to a dual 8P8C receptacle. My original purpose in making this card was to do some C-128 software development in the Kowalski simulator and then ship the results from my UNIX box to the C-128 via high speed serial interface. However, I set aside the project because it looked like it would be time wasted on a system that seemed to be rapdily "sunsetting." Also, POC was in existence, so I focused on that instead of C-128 stuff.

The UART card uses a 16V8 GAL for glue logic and as far as I can tell, does work. I also started on developing a ROM to go with the card that plugs into the C-128's empty ROM socket and automatically wedges a driver in the kernel at boot time. I got as far as getting the initialization functions to work, plus printing a banner on the screen. It probably could be made to work with a C-64, since the cartridge port functions for the two machines are identical.

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