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

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Page References

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SDMCTL
SDMCTL

Version management

Difference between version and

At line 1 added 3 lines
%%tabbedSection
%%tab-english
At line 7 added one line
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:
At line 9 added 23 lines
||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].
----
/%
%%tab-deutsch
||R/W||ADR||HEXADR||NAME||DESCRIPTION||OS||SHADOW||DEFAULT
|read/write|559|$022F |SDMCTL|Direct Memory Access (DMA) Control|all|[DMACTL]|34/$22
At line 47 added 11 lines
Zum Einschalten des Display List Interrupts siehe [NMIEN].
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/%
see also: [Player Missile Topics|Pm_topics], [Display List Topics|Displaylist_topics]
previous: [CDTMF5]
next: [SDLSTL],[SDLSTH|SDLSTL]
This page (revision-18) was last changed on 03-Feb-2023 15:21 by Jakub Husak  Top