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This page (revision-18) was last changed on 26-Sep-2022 11:39 by Jakub Husak  

This page was created on 09-Mar-2010 10:18 by Gromit

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%%tab-english
||R/W||ADR||HEXADR||NAME||DESCRIPTION||OS||SHADOW||DEFAULT
|read/write|559|$022F |SDMCTL|Direct Memory Access (DMA) Control|all|[DMACTL]|34/$22
This memory location is the shadow register of [DMACTL] (54272; $D400). It is used to control the [ANTIC]'s direct memory access ("DMA") to the memory of the Atari. The 6502 processor is halted during direct memory access. By switching the ANTIC's DMA off programs can be accelerated (approx. 30%). The following list shows how the individual bits of this register control the appearance of the screen:
||Bit||Dec||Hex||Function||Default
|7 | 128 | $80 | not used|0
|6 | 64 | $40 | not used|0
|5 |32| $20| Direct Memory Access on=1/off=0|1
|4| 16| $10| One-line P/M-vertical resolution on=1/off=0|0
|3| 8| $8| DMA for Players on=1/off=0|0
|2| 4| $4| DMA for Missiles on=1/off=0|0
|0,1| 3| $3| Wide playfield (48 bytes/chars)|
|0,1| 2| $2| Normal playfield (40 bytes/chars)|10
|0,1| 1| $1| Narrow playfield (32 bytes/chars)|
|0,1| 0| $0| Playfield off|
Bit #5 can therefore be used to control the entire direct memory access of the ANTIC. Bit #4 is used to switch between single-line P/M resolution and two-line resolution. The specification of the character width for the display playfield refers to the graphic mode 0. The numbers of characters correspond to 192, 160 or 128 color cycles. In total, the ANTIC can display 238 color cycles (including the border), but only about 174 of these are visible, depending on the TV/monitor. Therefore, not all 48 characters are completely visible when a wide display field is switched on (or the image extends beyond the edge of the monitor).
To switch on the Display List Interrupt see [NMIEN].
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Version Date Modified Size Author Changes ... Change note
18 26-Sep-2022 11:39 3.783 kB Jakub Husak to previous Added en translation
17 26-Sep-2022 11:24 2.023 kB Jakub Husak to previous | to last
16 20-Mar-2020 23:01 1.987 kB Florian Dingler to previous | to last
15 20-Mar-2020 22:58 1.927 kB Florian Dingler to previous | to last
14 25-Feb-2019 18:13 1.885 kB Florian Dingler to previous | to last
13 04-Sep-2015 00:11 1.774 kB Florian Dingler to previous | to last
12 18-Jul-2010 14:03 1.707 kB Florian Dingler to previous | to last
11 18-Jul-2010 14:03 1.71 kB Florian Dingler to previous | to last
10 10-May-2010 16:16 1.631 kB Gromit to previous | to last typo
9 16-Mar-2010 22:34 1.63 kB Florian Dingler to previous | to last
8 10-Mar-2010 11:07 1.56 kB Gromit to previous | to last
7 10-Mar-2010 11:05 1.558 kB Gromit to previous | to last
6 10-Mar-2010 11:04 1.554 kB Gromit to previous | to last
5 10-Mar-2010 10:25 1.598 kB Gromit to previous | to last
4 10-Mar-2010 10:24 1.596 kB Gromit to previous | to last
3 10-Mar-2010 10:23 1.545 kB Gromit to previous | to last
2 10-Mar-2010 09:48 1.497 kB Gromit to previous | to last
1 09-Mar-2010 10:18 1.635 kB Gromit to last
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