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Re: Need Help with some UARTs
Posted: Mon Jun 12, 2023 5:30 pm
by BigEd
The primary reason the 6501 pinout was changed was Motorola sued MOS Technology for patent infringement and as part of the settlement, the latter agreed to change the 6501 so it couldn't be plugged into an MC6800 board. The result was the “lawsuit-compatible” 6502.
Umm, the 6501 and 6502 were both introduced at the same time. The Moto lawsuit came later.
Re: Need Help with some UARTs
Posted: Mon Jun 12, 2023 7:11 pm
by Yuri
...
All members of the 6502 family have been designed to use a wired-OR interrupt circuit, excepting WDC’s 65C22S, which has a totem-pole IRQ output and hence can’t be wired-OR without the use of a blocking diode. A better implementation has the 65C22S driving one of the inputs of an AND gate, and another input of the same gate wired-OR to the other interrupting devices in the system. The gate’s output drives the IRQB pin on the MPU—no pullup resistor required.
That's where I got confused, this actually clarifies a bit for me. I was reading the details about 65C22S and getting them mixed up with the ones I have (which are the 65C22N).
So it does look like for the variety of 65C22's that I have, I will need to use the wire-or method. This isn't a problem of course, but it's good to know.
This of course leaves me with the question of if I should wire my 16550 directly to the wire-or chain, keep it on the 65C22's CA1 pin (part of me feels weird leaving it like this), or come up with some other interrupt controller. (But that's a topic for a different thread I think)