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| From: siz (all posts)
Date: 1999-03-19
Subject: Re: Lightpen
|
On Thu, 18 Mar 1999, Siz wrote:
> > Yesterday midnight I checked out the programs for the lightpen. I
> > was not able to figure out how horizontal position is being
> > measued. Vertical easy, when the sign coming in from the pen
> > (joybutton press), then it simply reads $FF1D.
>
> Hm. I didn't use my plusy 4 years ago... So I might remember incorrectly.
>
> There are two TED registers (probably $FF1E and $FF1F) containing the
> current raster line position.
Hm. I missed it. $FF1C and $FF1E is the vertical and $FF1E is the horizontal. but it's shifted one bit right, so the least significant bit is not present.
> > button read. (That I heard once.) But: reading $FD0D? Is this some
> > kind of mirroring $FF08? Or a direct read from the joy?
>
> From $FD00 to $FD0F there is the ACIA address range (it's only 4 registers
> really but they are mirrored to 16). The ACIA is the serial interface in
> the plus/4 that's available on the user port.
Yes. I looked for it and found. $FD0D is the "Program-Reset/Status"
register of the ACIA. (Program reset for writing and status for reading)
It's layout:
Bit Description
7 ACIA IRq
6 DSR
5 DCD
4 Transmit Data Register empty
3 Receive Data Register full
2 Overrun error *
1 Framing error *
0 Parity error *
* These bits don't generate IRq
>From these the DSR and the DCD are present on the user port connector (DSR is on pin L and DCD is on pin H).
Source: Gaspar Denes, Gyenes Tamas: A plus/4 belso felepitese. :)
--
Szell Imre (Siz)
siz@adam.hu
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