Re: A86: Linking Routines

To: assembly-86@lists.ticalc.org
Subject: Re: A86: Linking Routines
From: rabidcow@juno.com (Joshua J Seagoe)
Date: Fri, 15 Jan 1999 22:14:15 -0800
Delivered-To: assembly-86-outgoing@towerguard.unix.edu.sollentuna.se
Reply-To: assembly-86@lists.ticalc.org

there are two signal lines in the link cable.  when no data is being
transmitted, both lines are high.  to send a bit, the calc brings one
line low (depending on whether it's a 0 or a 1) and waits for the other
to go low.  then it returns it to high and waits for the other to return
to high.

to recieve a bit, wait for either line to go low.  when it does, note
which it is and determine whether it represents a 1 or a 0, then send the
other line low.  wait for return to high and send it like the other one
is expecting.

this is done 8 times to send/recieve a byte.
if nothing happens or if the other end brings both lines low for a long
enough time, an error is signalled and transmission is cancelled.

in the normal calc transfers, information is arranged into messages which
have a 4 byte header that tells who's sending it, what kind of message it
is, and when necessary, the size of the data sent with it.  there are
very specific "conversations" that the calculator expects and any
deviation will result in a transmission error.

what you're probly gonna have to do is periodically check the port to see
if either line is low, and if it is, read and interpret the data.  work
out some "language" to use and treat it almost like you're reading a
file.

if you're willing to write your own link routines, there's no reason you
have to work in bytes!  

-josh

On Fri, 15 Jan 1999 20:50:07 EST Jkhum98@aol.com writes:
>
>I need some assistence on learing how to use Linking Routines.  First 
>of all,
>are the Sendbyte and Getbyte Routines from ACZ too 86 specific?  I 
>would like
>to use them across all of the z80 calcs for the TCPA Battleship 
>project I'm
>working on... Well, I understand the input and output of these 
>routines, but I
>cant really grasp the concept of the linking yet... :\  How do the 
>calcs know
>which byte was transmitted, and how to store it to its corrosponding 
>spot in
>the two 64 byte tables i need transferred.  How is the data being
>sent/received, timed and lined up...? Somebody please give me an 
>explanation
>on how this works... I dont want to hear "Go check out the Ztetris 
>Source"
>though... =P  Also, get very technical about how the ports work, if 
>you
>must... Thanks in advance, anybody... =)
>															--Jason 
>K.
>

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