Re: Apple II lores GR "movies"

[David Wilson <david@uow.edu.au>]

"frank_bklyn" <frank_o_rama@hotmail.com> writes:
>Tell me more about the POKE $10 thing. my first impression is that it's
>probably a hoax. but if it's true, i could actually run at like 20
>frames per second or something. interestingly enough, 115k is faster
>than the keyspan USB-serial adapter I have on my G4 will run! (probably
>why i think the apple can't actually go that fast.)

It works - The 6551 has 16 different baud rate settings of which 15 give
"standard" data rates when a 1.8432MHz crystal is used. The remaining
setting just uses the raw clock divided by 16.

CR	div	baud rate = 1843200/div
$10	16	115200
$11	36864	50
$12	24576	75
...
$1d	256	7200
$1e	192	9600
$1f	96	19200

If you want a faster speed you can replace the 1.8432MHz crystal with
a faster one - according to the Rockwell databook I am looking at the
R6551 can handle crystals up to 2.5MHz (400ns Tccy) which would give
very non-standard baud rates. Even the R65C51 lists the same upper frequency
which is a pity as 3.6864MHz would allow the use of all the useful standard
bit rates.

Of course an unaccelerated Apple II/II+/IIe might have difficulty keeping
up with bytes arriving at the rate of one every 86 microseconds.
-- 
David Wilson  School of IT & CS, Uni of Wollongong, Australia