A82: Re: Reset of keyboard

To: <assembly-82@lists.ticalc.org>
Subject: A82: Re: Reset of keyboard
From: "Dines Justesen" <dines@aub.dk>
Date: Thu, 16 Mar 2000 21:58:03 +0100
References: <Pine.OSF.4.02.10003161134240.31057-100000@vega.utc.fr>
Reply-To: assembly-82@lists.ticalc.org


You should use a nop between a write and a read to ensure that the output is
updated before you read it. The ROM writes ff to the port after each read,
but whether this is necesaary as long as a nop is used i do not know. Have a
look at 1B8 to see how the ROM reads the port.

To my knowledge no one has done any real investigation on port timing
problems, but except for the display controller, doing what TI does should
be fine. There is also a slight change that the same kind of problems kan
happen on the link port, so remember to use the same amount of delay as the
ROM does.

Dines
----------------------------------------------------------------------
 Dines Justesen
 "ua mau ke ea o ka ai·na i ka po·no"
 dines@aub.dk
 www.student.dtu.dk/~c958362
----------------------------------------------------------------------

----- Original Message -----
From: "Eric Piel" <pieleric@etu.utc.fr>
To: <assembly-82@lists.ticalc.org>
Sent: Thursday, March 16, 2000 11:39 AM
Subject: A82: Reset of keyboard


>
> Hi
> Writing additional code in the Key handler of BMMP I remind the fact that
it is
> necesary to reset the keyboard port by sending ff before every scanning.
> for instance:
>         ld a,0ffh ; reset keyport
>         out (P_KEYBOARD),a ; necessary code?
> ld a,%11101111
> out (P_KEYBOARD),a ; Mask out 0/4
> in a,(P_KEYBOARD)
>
> I'd like to know if it has to be send every time or not and why.
> BTW has someone done more advance investigations about this subject?
>
> Eric
>
>

References:

A82: Reset of keyboard

From: Eric Piel <pieleric@etu.utc.fr>