Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Posting-Version: version B 2.10 5/3/83; site teklabs.UUCP
Path: utzoo!linus!decvax!tektronix!tekchips!teklabs!paulba
From: paulba@teklabs.UUCP
Newsgroups: net.micro.6809
Subject: DMA in SAM chip...
Message-ID: <2492@teklabs.UUCP>
Date: Mon, 26-Sep-83 17:03:26 EDT
Article-I.D.: teklabs.2492
Posted: Mon Sep 26 17:03:26 1983
Date-Received: Wed, 28-Sep-83 06:59:59 EDT
Organization: Tektronix, Beaverton OR
Lines: 23


	In the Motorola Microprocessor Data Manual there is a reference
to the DMA mode of the SAM chip.  (What is DMA in a dynamic ram controller ? )
Well, I tried setting the SAM to this mode.  Then the video became very
strange.  It seems to use about 8k of ram for video in PMODE 4.
Unfortunately this is a very strange memory map where the left
border is in increments of 42 (vertically).  It is very colorful though.
Has anyone else played with this mode ?
It is probably similar to PMODE 4,X : SCREEN 1,X : PMODE 3,X funny business.

PMODE 4,X : SCREEN 1,X : POKE &HFFC1,0
will get you there.


	Another SAM register for FAST processor usage is POKE &HFFD9,0.
The video goes nuts as there is NO time for the 6847 to use video for
display, the processor gets it all of the time.  This mode is NOT address
dependant like the FAST mode usually used.  If you don't care
what the video looks like at this time, then it is useable.  For myself
I don't really like the video scrambled while running a program.
To restore this mode to SLOW,   POKE &HFFD8,0   does it.

			teklabs!paulba