If you are told to use an 8255 refuse, if the refusal does not work, stamp your little feet in the ground, if that does not work, go cry. Then do as your suprevisor or teacher tell you to do and CLARLY mark all schematics with "8255 used under protest"

I doubt very much that you've ever taken time to determine whether you even need that last level of performance.
if I did not need the (I/O) speed, I would use a cheaper processor. The earlier, less flexible models did have a cheaper processor (the 668).

you'd already have known (a) that the F12x-series supports an external bus, and (b) that the external bus cycles can be extended to match the peripheral that's out there.
That is insulting - of course I know that. BUT I need a 10MHz bitstream with clock, do THAT with your stupid antique.

I don't believe you can come up with a circuit that operates reliably with your favorite MCU, even with HC logic without slowing down the MCU
setb port pin 20ns
clr port pin 20ns
40 nanoseconds total and a latch is clocked with a 20ns clock pulse width which any HCT chip is happy with.

so an actual example
rrc a 10ns
movc p1_data bit,C 20ns
setb P1_clock_bit 20ns
clr P1_clock_bit 20ns
serial bitstream at 70ns including 3 I/O instructions now come up with a way yo that with the slowpoke. NO, I do not want to hear about mode 0, the UARTs are already in use. This stated because it would be typical of you to state a defense of "the usefulness of the 8255" by saying something about mode 0, talk about "red herrings".

Further, I doubt very much that YOU can come up with a circuit that provides the functions of an 8255, regardless of what sort of logic you have at your disposal.
CAN't YOU READ
in my previous post I wrote I can "come up with a positive construct" to any place where you and other antique collectors would use an 8255 if you would state WHAT FOR.
Now again you go for some fuzzy unspecified "the functions of an 8255"

Anyone willing to do the simple arithmetic can make the 8255 work with the F12x-series of SiLabs parts without slowing down anything other than the external bus cycles that "talk" to the 8255's that are attached.
If you are going to slow it down anyhow, why not save some money and buy a cheap slowpoke derivative

Anyone except you, of course, since, in your case, it's just a matter of having your head in the sand. Why do you suppose the SiLabs guys provided these functions that extend the external bus cycles without slowing down the processor for any other cycles?
to make YOU happy :) . As a matter of fact I have a flash that is "written twice a year, read twice an hour" for which I double the memory bus cycle time.
Now since we are playing the "why do you suppose" game, "why do you suppose" th3e derivatives are availble with 8 ports?

The issue here is that if you flip a bit once an hour, who cares about the time it takes, but for real work it DOES matter.

Erik