[A86] Re: The f'n 86 screen
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[A86] Re: The f'n 86 screen
My understanding was that when reading from port 3:
bit 0 is set if this interrupt was generated by the on key
bit 1 is set if the interrupt was generated by the 200/s signal
bit 3 is set if the on key is currently being pressed
So if bits 0 and 1 are both clear, then some other misterious source has
generated an interrupt. I had assumed that this was from the keyboard,
but that looks wrong. (The rom just responds by sending $0b to port 3
and returning, not by checking the keyboard.) Tho iirc, if you don't
skip the grayscale code on these "unknown" interrupts, you get flashes
when you press keys... bah, I'm too lazy to get out my link cable ;)
The refresh *is* connected to the 200/s interrupt somehow, you can see
that because the flicker effect scrolls when you don't use halts to
syncronize to it.
I have to wonder when those bits would get cleared... maybe when writing
to the port?
> bit 1,a ;if bit 1 set (equal to 1)
> jr z,leave_int ;leave interuppt
Ok, I may just be confused, but this comment seems wrong.
Doesn't the "bit" instruction set the zero flag if the bit is zero?
If so, that would jump if the bit was *clear*...
-josh
On Mon, 01 Oct 2001 16:50:23 -0400 Ricky Cobb <arcadesdude@operamail.com>
writes:
>
> I _think_ you read bit 1 of port 3 to see if the
> screen update is in progress and leave the interuppt
> if it is (if bit 1 is set).
>
> This code is from Dux Gregis' Blitzgry IM2 4-Level
> Grey-scale routine. This is only a snippit; the full
> code can be found here:
>
> http://guide.ticalc.org/advanced/gray.htm
>
> and here.
>
> http://www.ti-programmers.com/cgi-
> bin/ultimatebb.cgi?ubb=get_topic&f=4&t=000001
>
> (different explainations)
>
etc.
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