Internal Port Decoding b0-7 Register

Next Register Number	$82
Readable	Yes
Writable	Yes
Short Description	Enabling internal ports decoding

Bit	Description
7	Enabling IO:$xx37 (also MD2 controller)
6	Enabling IO:$xx1F (also MD1 controller)
5	Enabling IO:$xx6B
4	Enabling +3 floating bus
3	Enabling IO:$1FFD
2	Enabling IO:$DFFD
1	Enabling IO:$7FFD
0	Enabling IO:$xxFF

All bits are set to 1 upon soft reset.

The internal port decoding enables always apply.

When the expansion bus is on, the expansion port decoding (Next Registers $86-$89) enables are logically ANDed with the internal enables (Next Registers $82-$85). A zero bit indicates the internal device is disabled.

If the expansion bus is on, this allows I/O cycles for disabled internal ports to propagate to the expansion bus, otherwise corresponding I/O cycles to the expansion bus are filtered.

(note: Next registers with number higher than $7F are inaccessible from Copper code)