Date   : Tue, 27 Apr 2004 10:07:19 +0100
From   : Richard_Talbot-Watkins@...
Subject: Re: Analogue Port Fire Buttons

Tom Walker wrote:

> Nope! The fire buttons are just connected to port B
> bits 4 and 5. I don't even think interrupts need to be
> disabled.

Yes, I think the BBC OS guarantees:

- port B bits 0-3: outputs (addressable latch)
- port B bits 4-5: inputs  (fire buttons)
- port B bits 6-7: inputs  (speech processor)

via setting ?&FE42 to &0F.

so, provided this is true, it should be possible to read
from &FE40 without needing to disable interrupts to
determine the fire button status.

(?&FE40 AND 16) = 0  : fire button 1 pressed
                <> 0 : fire button 1 released

(?&FE40 AND 32) = 0  : fire button 2 pressed
                <> 0 : fire button 2 released

Rich



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