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System RAM - Intellivision Wiki

System RAM


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(mention bus copy)
(mention the video FIFO)
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The System RAM unit is the only 16-bit RAM available in the Intellivision, and it is mapped into the Intellivision [[Memory Map|memory map]] from $0200-$035F.  The System RAM has the additional responsibility of bridging between the STIC's private graphics bus and the CPU's main memory bus.  This additional functionality is described under [[Bus Copy]].<br /><br />
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The System RAM unit is the only 16-bit RAM available in the Intellivision, and it is mapped into the Intellivision [[Memory Map|memory map]] from $0200-$035F.  The System RAM has the additional responsibilities:
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* It bridges between the STIC's private graphics bus and the CPU's main memory bus.  This additional functionality is described under [[Bus Copy]].
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* It provides a 20-word Video FIFO to reduce the STIC's [[STIC Bus Request|memory bandwidth impact]] on the System RAM.
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<br />
Programs which rely heavily on the [[Executive ROM]] cannot use most of the storage in System RAM.  The display background occupies most of System RAM, and the EXEC's variables and data structures occupy the rest.  Some EXEC-based games do store variables here through various tricks, such as limiting the number of active MOBs to fewer than 8, or by blanking the first row of the display to make $200 - $213 available.  (Advanced Dungeons and Dragons Tarmin Treasure does the latter trick.)  Programs that utilize the EXEC minimally, if at all can allocate all of $2F0 - $35F as they see fit.<br /><br />
Programs which rely heavily on the [[Executive ROM]] cannot use most of the storage in System RAM.  The display background occupies most of System RAM, and the EXEC's variables and data structures occupy the rest.  Some EXEC-based games do store variables here through various tricks, such as limiting the number of active MOBs to fewer than 8, or by blanking the first row of the display to make $200 - $213 available.  (Advanced Dungeons and Dragons Tarmin Treasure does the latter trick.)  Programs that utilize the EXEC minimally, if at all can allocate all of $2F0 - $35F as they see fit.<br /><br />

Revision as of 09:16, 11 January 2005

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