Re: A83: Re: fwd: re: TI-83 port 2

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Re: A83: Re: fwd: re: TI-83 port 2


On 17-Jun-98, Florent Dhordain wrote:

>    Could you explain this more precisely ? I mean, which bits do what ?

>I think these ports works this way :

>Port 3 R/W
> R : bit 0 : [on] key pressed
> R : bit 1 : periodic interrupt occured ( called VBI by Dines )
> R : bit 2 : 2nd interrupt occured ( what does it does ? batteries are
checked
>when it occurs )
> R : bit 3 : Status : bit 0 xor bit 1 xor bit 2 ???
> W : bit 0 : [on] int mask
> W : bit 1 : periodic int mask
> W : bit 2 : 2nd interrupt int mask
> W : bit 3 : LCD standby when reset.
>I think int are enable when mask =1. After a int has occured, you must reset
>the
>mask, and set it again, right ?

I'm always checking bit 3 of port 3 to see whether the on key is pressed. This
wrong?

>Port 4 W  ???R???
> W : bit 0 : ???? (freezes calc when set, but used...)
> W : bit 1 : ????
> W : bits 2 & 3 : select interrupt speed ( $11 : normal, $00 fastest )
> W : bits 4..7 : select battery check threshold ???

>Port 14 : R ???W???
> R : bit 0 : battery state (Good/fair). See threshold

Yeah, but when you read port 14 you get 31d, which is rather an odd number to
get if only one bit is useful. But yes, ti-os is only checking bit 0.

>Could you tell me if I'm right, or what they're used for ? And what is the
>other
>int used for ?
>I've also got some troubles with port 0 : what are bits 0 1 5 6 7(in read)
and
>2
>3 5 6 7(in write) used for ?
>And with port 2 : bits 3 4 5 6 7 ?

My guess is that the upper bits of port 2 control the rom page available in
0000-3fff. But why are bits 3 and 7 unused when some bits in port 0 are used
to select rom pages aswell? Wouldn't it be simpler if the whole lower nibble
of port 2 controlled the page number? Or am I missing something?

>And, the ports access only uses bits 4 2 1 0, so port $18= port $10, port
>$29=port 1 ?

Yep.

>I know, I ask a lot, but it would really help to understand the ti83 hardware
>more precisely... for better emulators, and for better games

>- Florent



>------------------
>Original text

>From: Pat Milheron <pmilheron@ti.com>, on 6/17/98 11:06 AM:
>To: lairfight@softhome.net

>Port 3 is the interrupt status port.
>Port 4 is the system configuration port, configures the asic.
>Port 14h is used for low battery detection.

>Later,
>Pat
>----------
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