Re: [stella] 65xx Questions

Subject: Re: [stella] 65xx Questions
From: Manuel Polik <cybergoth@xxxxxxxx>
Date: Mon, 08 Jul 2002 19:31:21 +0200
Hi Paul!

>1) What is the difference between overflow and carry?

In short, 

Carry    is the 9th bit
Negativ  is the 8th bit
Overflow is the 7th bit

You can do funny stuff with the Overflow.
Assuming you'd use the seventh Bit off foo as bolean 
bitswitch, you could do:

BIT foo
BVS True

for example :-)

>2) What are some common situations where EOR is useful?

Hm... some standard VCS jobs for EOR:

- To flip a bitswitch
- To invert a certain bitpattern
- Generate Random numbers
- Invert the readings from the joystick port
- Generate screensaver colors

I'm using it quite often in Gunfight too. There's some 
tricky EOR code for simplyfying the PF/Missile collision 
detection in it for example...


Archives (includes files) at
Unsub & more at

Current Thread