5 Sep
2001
5 Sep
'01
2:12 a.m.
Until I get my hands on a copy of the venerable
"Beneath Apple Dos"
is there anyone who can point me to an online resource describing the
Apple ][ disk controller P6 ROM state machine? The exact uses
for the Q6 and Q7 switches ($C0EC-$C0EF)? Or would be willing to
summarize from the mighty tome for me?
From:
http://www.mac.linux-m68k.org/devel/iwm.php
: =======================
: Accessing IWM Registers
: =======================
: The IWM chip has several internal registers available to programs.
: Access to these registers is controlled by the Q6 and Q7 switches.
:
: +=====+=====+=======================================+
: | Q6 | Q7 | Register |
: +=====+=====+=======================================+
: | off | off | Read data register |
: +-----+-----+---------------------------------------+
: | off | on | Read handshake register |
: +-----+-----+---------------------------------------+
: | on | off | Read status register |
: +-----+-----+---------------------------------------+
: | on | on | Write mode register (if drive is off) |
: | | | data register (if drive is on) |
: +-----+-----+---------------------------------------+
:
: The mode register is a write-only register containing several flag bits
: which control various features if the IWM. To access it, turn off the
: drive (by accessing ENABLE), turn on Q6 and Q7, and write to any
: odd-numbered address in the $C0E0...$C0EF range.
hth,
-dq